Catálogo de publicaciones - revistas

<jats:p>We theoretically analyze the photon number distribution, entanglement entropy, and Wigner phase-space distribution, considering the finite-dimensional pair coherent state (FDPCS) generated in the nonlinear Bose operator realization. Our results show that the photon number distribution is governed by the two-mode photon number sum <jats:italic>q</jats:italic> of the FDPCS, the entanglement of the FDPCS always increases quickly at first and then decreases slowly for any <jats:italic>q</jats:italic>, and the nonclassicality of the FDPCS for odd <jats:italic>q</jats:italic> is more stronger than that for even <jats:italic>q</jats:italic>.</jats:p>

<jats:p>The atomistic Green’s function method is improved to compute the polarization resolved phonon transport in a multi-terminal system. Based on the recent developments in literature, the algorithm is simplified. The complex phonon band structure of a semi-infinite periodic terminal is obtained by the generalized eigenvalue equation. Then both the surface Green’s function and phonon group velocity in the terminal are determined from the wave modes propagating away from the scattering region along the terminal. With these key ingredients, the individual phonon mode transmittance between the terminals can be calculated. The feasibility and validity of the method are demonstrated by the chain example compared with the wave packet method, and an example of graphene nanojunction with three terminals.</jats:p>

<jats:p>We employ molecular dynamic simulation to investigate metabasin dynamics for supercooled polymer melt. We find that, in a small system, the <jats:italic>α</jats:italic>-relaxation process is composed of a few crossing events that the monomers hops from one metabasin to another. Each crossing event is very rapid and involves a democratic movement of many particles, whereas such collective motion is not string-like. Evaluation on the contributions of metabasin exploration and democratic movement shows that the structural relaxation is mostly governed by the latter. Our calculated results show that the metabasin–metabasin transitions are not the main reason of spatially dynamical heterogeneity. It is different from the binary Lennard–Jones mixture model in which the metabasin–metabasin transitions are relevant for the spatially dynamical heterogeneity.</jats:p>

<jats:p>Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals. In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry tilt grain boundary (ATGB) under shock-loading is performed. We find that the shock response of asymmetric grain boundaries is quite different from that of symmetric grain boundaries. Especially, our simulation proves that shock can induce migration of asymmetric grain boundary in iron. We also find that the shape and local structure of grain boundary (GB) would not be changed during shock-induced migration of Σ3 [110] ATGB, while the phase transformation near the GB could affect migration of GB. The most important discovery is that the shock-induced shear stress difference between two sides of GB is the key factor leading to GB migration. Our simulation involves a variety of piston velocities, and the migration of GB seems to be less sensitive to the piston velocity. Finally, the kinetics of GB migration at lattice level is discussed. Our work firstly reports the simulation of shock-induced grain boundary migration in iron. It is of great significance to the theory of GB migration and material engineering.</jats:p>

<jats:p>We conducted <jats:italic>in-situ</jats:italic> high-pressure synchrotron x-ray diffraction (XRD) and electrical transport measurements on Dirac-like semimetal PdSn<jats:sub>4</jats:sub> in diamond anvil cells with quasi-hydrostatic pressure condition up to 44.5 GPa–52.0 GPa. The XRD data show that the ambient orthorhombic phase (<jats:italic>Ccca</jats:italic>) is stable with pressures to 44.5 GPa, and the lattice parameters and unit-cell volume decrease monotonously upon compression. The temperature dependence of the resistance exhibits a metallic conduction and follows a Fermi-liquid behavior below 50 K, both of which keep unchanged upon compression to 52.0 GPa. The magnetoresistance curve at 5 K maintains a linear feature in a magnetic field range of 2.5 T–7 T with increasing pressure to 20.0 GPa. Our results may provide pressure-transport constraints on the robustness of the Dirac fermions.</jats:p>

<jats:p>In recent years, accelerating waves have attracted great research interests both due to their unique properties and tempting applications. Here we investigate the effect of the inter-particle interaction on accelerating of Bose–Einstein condensate (BEC). We show that spatially homogeneous interactions will have no accelerating effect on BEC regardless of the interaction form (contact, dipole–dipole, or any others). But spatially inhomogeneous interactions may lead to an accelerating motion of the condensate. As an example, the accelerating dynamic of BEC under a spatially linear modulated contact interaction is studied in detail. It is found that such an interaction will accelerate the condensate with a time varying acceleration. Furthermore, an interaction engineering scheme to achieve constantly accelerating BEC is proposed and studied numerically. Numerical results suggest that this engineering scheme can also suppress profile changing of the condensate during its evolution, thus realize an accelerating profile-keeping matter wave packet. Our analysis also applies to optical waves with Kerr nonlinearity.</jats:p>

<jats:p>The novel BaTiO<jats:sub>3</jats:sub>/BiFeO<jats:sub>3</jats:sub>/TiO<jats:sub>2</jats:sub> multilayer heterojunction is prepared on a fluorine-doped tinoxide (FTO) substrate by the sol–gel method. The results indicate that the Pt/BaTiO<jats:sub>3</jats:sub>/BiFeO<jats:sub>3</jats:sub>/TiO<jats:sub>2</jats:sub>/FTO heterojunction exhibits stable bipolar resistive switching characteristic, good retention performance, and reversal characteristic. Under different pulse voltages and light fields, four stable resistance states can also be realized. The analysis shows that the main conduction mechanism of the resistive switching characteristic of the heterojunction is space charge limited current (SCLC) effect. After the comprehensive analysis of the band diagram and the <jats:italic>P</jats:italic>–<jats:italic>E</jats:italic> ferroelectric property of the multilayer heterojunction, we can deduce that the SCLC is formed by the effect of the oxygen vacancy which is controlled by ferroelectric polarization-modulated change of interfacial barrier. And the effective photo-generated carrier also plays a regulatory role in resistance state (RS), which is formed by the double ferroelectric layer BaTiO<jats:sub>3</jats:sub>/BiFeO<jats:sub>3</jats:sub> under different light fields. This research is of potential application values for developing the multi-state non-volatile resistance random access memory (RRAM) devices based on ferroelectric materials.</jats:p>

<jats:p>The migration of lanthanide fission products to cladding materials is recognized as one of the key causes of fuel–cladding chemical interaction (FCCI) in metallic fuels during operation. We have performed first-principles density functional theory calculations to investigate the segregation behavior of lanthanide fission products (La, Ce, Pr, and Nd) and their effects on the intergranular embrittlement at Σ3(111) tilt symmetric grain boundary (GB) in <jats:italic>α</jats:italic>-Fe. It is found that La and Ce atoms tend to reside at the first layer near the GB with segregation energies of −2.55 eV and −1.60 eV, respectively, while Pr and Nd atoms prefer to the core mirror plane of the GB with respective segregation energies of −1.41 eV and −1.50 eV. Our calculations also show that La, Ce, Pr, and Nd atoms all act as strong embrittlers with positive strengthening energies of 2.05 eV, 1.52 eV, 1.50 eV, and 1.64 eV, respectively, when located at their most stable sites. The embrittlement capability of four lanthanide elements can be determined by the atomic size and their magnetism characters. The present calculations are helpful for understanding the behavior of fission products La, Ce, Pr, and Nd in <jats:italic>α</jats:italic>-Fe.</jats:p>

<jats:p>An ultra-high voltage 4H-silicon carbide (SiC) gate turn-off (GTO) thyristor for low switching time is proposed and analyzed by numerical simulation. It features a double epitaxial p-base in which an extra electrical field is induced to enhance the transportation of the electrons in the thin p-base and reduce recombination. As a result, the turn-on characteristics are improved. What is more, to obtain a low turn-off loss, an alternating p<jats:sup>+</jats:sup>/n<jats:sup>+</jats:sup> region formed in the backside acts as the anode in the GTO thyristor. Consequently, another path formed by the reverse-biased n<jats:sup>+</jats:sup>–p junction accelerates the fast removal of excess electrons during turn-off. This work demonstrates that the turn-on time and turn-off time of the new structure are reduced to 37 ns and 783.1 ns, respectively, under a bus voltage of 8000 V and load current of 100 A/cm<jats:sup>2</jats:sup>.</jats:p>

<jats:p>We theoretically investigate the strong coupling in silver-molecular J-aggregates-silver structure sandwiched between two dielectric media by using classical methods. Fresnel equations are employed to solve our proposed structure. The results show that both the reflection and transmission spectra show a Rabi splitting-like line shape, revealing the strong coupling phenomenon. Furthermore, the radiative angle <jats:italic>versus</jats:italic> incident wavelength exhibits a Fano line shape. The strong coupling phenomenon can be well tuned by controlling the surface plasmon excitation, such as the incident angle and the thickness of the silver films. Our structure has potential applications in quantum networks, optical switches, and so on.</jats:p>