Catálogo de publicaciones - revistas

<jats:p>Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.</jats:p>

<jats:p>We demonstrate visible-light all-fiber vortex lasers by incorporating the home-made mode selective couplers (MSCs). The MSC at green or red wavebands is fabricated by specially designing and fusing a single-mode fiber (SMF) and a few-mode fiber (FMF). The MSCs inserted into visible fiber cavities act as power splitters and mode converters from the LP<jats:sub>01</jats:sub> to LP<jats:sub>11</jats:sub> mode at green and red wavelengths, respectively. The red-light all-fiber vortex laser is formed by a 10-cm Pr<jats:sup>3+</jats:sup>/Yb<jats:sup>3+</jats:sup>:ZBLAN fiber, a fiber Bragg grating, a fiber end-facet mirror and the MSC at 635 nm, which generates vortex beams with OAM<jats:sub>±1</jats:sub> at 634.4 nm and an output power of 13 mW. The green-light all-fiber vortex laser consists of a 12-cm Ho<jats:sup>3+</jats:sup>:ZBLAN fiber, two fiber pigtail mirrors, and the MSC at 550 nm, which generates vortex beams with OAM<jats:sub>±1</jats:sub> at 548.9 nm and an output power of 3 mW.</jats:p>

<jats:p>We proposed a vanadium dioxide (VO<jats:sub>2</jats:sub>)-integrated multi-functional metamaterial structure that consists of three metallic grating layers and two VO<jats:sub>2</jats:sub> films separated by SiO<jats:sub>2</jats:sub> dielectric spacers. The proposed structure can be flexibly switched among three states by adjusting temperature, incident direction, and polarization. In state 1, the incident wave is strongly transmitted and perfectly converted to its orthogonal polarization state. In state 2, the incident wave is perfectly absorbed. In state 3, incident wave is totally reflected back. The working frequency of the multi-functional metamaterial can be arbitrarily tuned within a broad pass band. We believe that our findings are beneficial in designing temperature-controlled metadevices.</jats:p>

<jats:p>Pre-warning plays an important role in emergency handling, especially in urban areas with high population density like Beijing. Knowing the information dissemination mechanisms clearly could help us reduce losses and ensure the safety of human beings during emergencies. In this paper, we propose the models of pre-warning information dissemination via five classical media based on actual pre-warning issue processes, including television, radio, short message service (SMS), electronic screens, and online social networks. The population coverage ability and dissemination efficiency at different issue time of these five issue channels are analyzed by simulation methods, and their advantages and disadvantages are compared by radar graphs. Results show that SMS is the most appropriate way to issue long-term pre-warning for its large population coverage, but it is not suitable for issuing urgent warnings to large population because of the limitation of telecom company’s issue ability. TV shows the best performance to combine the dissemination speed and range, and the performance of radio and electronic screens are not as satisfactory as the others. In addition, online social networks might become one of the most promising communication method for its potential in further diffusion. These models and results could help us make pre-warning issue plans and provide guidance for future construction of information diffusion systems, thus reducing injuries, deaths, and other losses under different emergencies.</jats:p>

<jats:p>Hall thruster is an electric propulsion device for attitude control and position maintenance of satellites. The discharge process of Hall thruster will produce divergent plume. The plume will cause erosion, static electricity, and other interference to the main components, such as solar sailboard, satellite body, and thruster. Therefore, reducing the divergence of the plume is an important content in the research of thruster plume. The additional electrode to the plume area is a way to reduce the divergence angle of the plume, but there are few related studies. This paper uses the particle-in-cell (PIC) simulation method to simulate the effect of the additional electrode on the discharge of the Hall thruster, and further explains the effect mechanism of the additional electrode on parameters such as the electric field and plume divergence angle. The simulation results show that the existence of the additional electrode can enhance the potential near the additional position. The increase of the potential can effectively suppress the radial diffusion of ions, and effectively reduce the plume divergence angle. The simulation results show that when the additional electrode is 30 V, the half plume divergence angle can be reduced by 18.21%. However, the existence of additional electric electrode can also enhance the ion bombardment on the magnetic pole. The additional electrode is relatively outside, the plume divergence angle is relatively small, and it can avoid excessive ion bombardment on the magnetic pole. The research work of this paper can provide a reference for the beam design of Hall thruster.</jats:p>

<jats:p>Compactness and miniaturization have become increasingly important in the development of high-power microwave devices. Based on this rising demand, a novel C-band coaxial transit-time oscillator (TTO) with a low external guiding magnetic field is proposed and analyzed. The proposed device has the following advantages: simple structure, short axial length, high power conversion efficiency, and low external guiding magnetic field, which are of great significance for developing the compact and miniaturized high-power microwave devices. The application of a shorter axial length is made possible by the use of a transit radiation mechanism. Also, loading the opening foil symmetrically to both ends of the buncher helps reduce the external magnetic field of the proposed device. Unlike traditional foils, the proposed opening foil has a circular-hole; therefore, the electron beam will not bombard the conductive foil to generate plasma. This makes it possible to realize long pulse and high repetition rate operation of the device in future experiments. Through numerical calculation and PIC particle simulation, the stability of the intense relativistic electron beam (IREB) and the saturation time of the device are improved by using the conductive foil. The voltage and current of the diode are 548 kV and 11.4 kA, respectively. Under a 0.4-T external guiding magnetic field, a C-band output microwave with a frequency of 4.27 GHz and power of 1.88 GW can be generated. The power conversion efficiency of the proposed device is about 30%.</jats:p>

<jats:p>The strengthening effects of alloying elements Re, Ta, and W in the [110] (001) dislocation core of the <jats:italic>γ</jats:italic> / <jats:italic>γ</jats:italic>′ interface are studied by first-principles calculations. From the level of energy the substitution formation energies and the migration energies of alloying elements are computed and from the level of electron the differential charge density (DCD) and the partial density of states (PDOSs) are computed. Alloying elements above are found to tend to substitute for Al sites <jats:italic>γ</jats:italic>′ phase by analyzing the substitution formation energy. The calculation results for the migration energies of alloying elements indicate that the stability of the [110] (001) dislocation core is enhanced by adding Ta, W, and Re and the strengthening effect of Re is the strongest. Our results agree with the relevant experiments. The electronic structure analysis indicates that the electronic interaction between Re-nearest neighbor (NN) Ni is the strongest. The reason why the doped atoms have different strengthening effects in the [110] (001) dislocation core is explained at the level of electron.</jats:p>

<jats:p>By applying the first principles calculations combined with density functional theory (DFT), this study explored the optical properties, electronic structure, and structure stability of triangular borophene decorated chemically, B<jats:sub>3</jats:sub> <jats:italic>X</jats:italic> (<jats:italic>X</jats:italic> = F, Cl) in a systematical manner. As revealed from the results of formation energy, phonon dispersion, and molecular dynamics simulation study, all the borophene decorated chemically were superior and able to be fabricated. In the present study, triangular borophene was reported to be converted into Dirac-like materials when functionalized by F and Cl exhibiting narrow direct band gaps as 0.19 eV and 0.17 eV, separately. Significant light absorption was assessed in the visible light and ultraviolet region. According the mentioned findings, these two-dimensional (2D) materials show large and wide promising applications for future nanoelectronics and optoelectronics.</jats:p>

<jats:p>Many complex networks in real life are embedded in space and most infrastructure networks are interdependent, such as the power system and the transport network. In this paper, we construct two cascading failure models on the multilayer spatial network. In our research, the distance <jats:italic>l</jats:italic> between nodes within the layer obeys the exponential distribution <jats:italic>P</jats:italic>(<jats:italic>l</jats:italic>) ∼ exp(–<jats:italic>l</jats:italic>/<jats:italic>ζ</jats:italic>), and the length <jats:italic>r</jats:italic> of dependency link between layers is defined according to node position. An entropy approach is applied to analyze the spatial network structure and reflect the difference degree between nodes. Two metrics, namely dynamic network size and dynamic network entropy, are proposed to evaluate the spatial network robustness and stability. During the cascading failure process, the spatial network evolution is analyzed, and the numbers of failure nodes caused by different reasons are also counted, respectively. Besides, we discuss the factors affecting network robustness. Simulations demonstrate that the larger the values of average degree 〈<jats:italic>k</jats:italic>〉, the stronger the network robustness. As the length <jats:italic>r</jats:italic> decreases, the network performs better. When the probability <jats:italic>p</jats:italic> is small, as <jats:italic>ζ</jats:italic> decreases, the network robustness becomes more reliable. When <jats:italic>p</jats:italic> is large, the network robustness manifests better performance as <jats:italic>ζ</jats:italic> increases. These results provide insight into enhancing the robustness, maintaining the stability, and adjusting the difference degree between nodes of the embedded spatiality systems.</jats:p>

<jats:p>In this paper, we investigate the effects of lattice strain on the electrical and magnetotransport properties of La<jats:sub>0.7</jats:sub>Sr<jats:sub>0.3</jats:sub>MnO<jats:sub>3</jats:sub> (LSMO) films by changing film thickness and substrate. For electrical properties, a resistivity upturn emerges in LSMO films, <jats:italic>i.e.</jats:italic>, LSMO/STO and LSMO/LSAT with small lattice strain at a low temperature, which originates from the weak localization effect. Increasing film thickness weakens the weak localization effect, resulting in the disappearance of resistivity upturn. While in LSMO films with a large lattice strain (<jats:italic>i.e.</jats:italic>, LSMO/LAO), an unexpected semiconductor behavior is observed due to the linear defects. For magnetotransport properties, an anomalous in-plane magnetoresistance peak (pMR) occurs at low temperatures in LSMO films with small lattice strain, which is caused by two-dimensional electron gas (2DEG). Increasing film thickness suppresses the 2DEG, which weakens the pMR. Besides, it is found that the film orientation has no influence on the formation of 2DEG. While in LSMO/LAO films, the 2DEG cannot form due to the existence of linear defects. This work can provide an efficient way to regulate the film transport properties.</jats:p>