Catálogo de publicaciones - revistas

<jats:p>The size reduction of atomic clocks is a long-standing research issue. Many atomic clocks such as passive hydrogen masers (PHMs) and compact rubidium masers (CRMs) use iris-loaded resonance cavities (IRCs) as their microwave cavities because they can dramatically reduce the radical sizes of the atomic clocks. In this paper, the electromagnetic characteristic of the IRC is investigated by a theoretical model based on electromagnetic field theory. The formulas to calculate the resonance frequency, quality factor, and magnetic energy filling factor are presented. The relationship between the IRC structure and its electromagnetic characteristic is clarified. The theoretical calculation results accord well with the electromagnetic software simulations and experimental results. The results in this paper should be helpful in understanding the physical mechanism of the IRC and designing the atomic clocks.</jats:p>

<jats:p>Bearing-based hunting protocols commonly adopt a leaderless consensus method, which requests an entire state of the target for each agent and ignores the necessity of collision avoidance. We investigate a hunting problem of multi-quadrotor systems with hybrid bearing protocols, where the quadrotor systems are divided into master and slave groups for reducing the onboard loads and collision avoidance. The masters obtain the entire state of the target, whose hybrid protocols are based on the displacement and bearing constraints to maintain formation and to avoid the collision in the hunting process. However, the slaves’ protocols merely depend on the part state of the masters to reduce loads of data transmission. We also investigate the feasibility of receiving the bearing state from machine vision. The simulation results are given to illustrate the effectiveness of the proposed hybrid bearing protocols.</jats:p>

<jats:p>Electric quadrupole moments of low-lying excited states of Yb<jats:sup>+</jats:sup> are calculated by relativistic coupled-cluster theory with perturbations from external fields. The field-dependent energy differentiation provides accurate values of the electric quadrupole moments of <jats:sup>2</jats:sup>P<jats:sub>3/2</jats:sub>, <jats:sup>2</jats:sup>D<jats:sub>3/2,5/2</jats:sub>, and <jats:sup>2</jats:sup>F<jats:sub>5/2,7/2</jats:sub> states which agree well with experimental values. The important role of the electronic correlation to the electric quadrupole moments is investigated. Our calculations indicate the early dispute of the electric quadrupole moment of the Yb<jats:sup>+</jats:sup>(<jats:sup>2</jats:sup>F<jats:sub>7/2</jats:sub>) state for which the measured and theoretical values have a large discrepancy. These electric quadrupole moment values can help us to determine the electric quadrupole shifts in start-of-the-art experiments of the Yb<jats:sup>+</jats:sup> ion.</jats:p>

<jats:p>In this work, we theoretically probe into the photo-induced hydrogen bonding effects between S0 state and S1 state as well as the excited state intramolecular proton transfer (ESIPT) behavior for a novel 2-[1,3]dithian-2-yl-6-(7 aH-indol-2-yl)-phenol (DIP) probe system. We first study the ground-state hydrogen bonding O–H⋯N behavior for DIP. Then we analyze the primary geometrical parameters (<jats:italic>i.e.</jats:italic>, bond length, bond angle, and infrared (IR) stretching vibrational mode) involved in hydrogen bond, and confirm that the O–H⋯N of DIP should be strengthened in the first excited state. It is the significant prerequisite for ESIPT reaction. Combining the frontier molecular orbitals (MOs) with vertical excitation analyses, the intramolecular charge transfer (ICT) phenomenon can be found for the DIP system, which reveals that the charge redistribution facilitates ESIPT behavior. By constructing potential energy curves for DIP along the ESIPT reactional orientation, we obtain quite a small energy barrier (3.33 kcal/mol) and affirmed that the DIP molecule undergoes ultrafast ESIPT process once it is excited to the S1 state and quickly transfers its proton, forming DIP-keto tautomer. That is why no fluorescence of DIP can be observed in experiment, which further reveals the ultrafast ESIPT mechanism proposed in this work.</jats:p>

<jats:p>Computer simulations were performed to study the dense mixtures of passive particles and active particles in two dimensions. Two systems with different kinds of passive particles (e.g., spherical particles and rod-like particles) were considered. At small active forces, the high-density and low-density regions emerge in both systems, indicating a phase separation. At higher active forces, the systems return to a homogeneous state with large fluctuation of particle area in contrast with the thermo-equilibrium state. Structurally, the rod-like particles accumulate loosely due to the shape anisotropy compared with the spherical particles at the high-density region. Moreover, there exists a positive correlation between Voronoi area and velocity of the particles. Additionally, a small number of active particles capably give rise to super-diffusion of passive particles in both systems when the self-propelled force is turned on.</jats:p>

<jats:p>Ammonium iodine (NH<jats:sub>4</jats:sub>I) as an important member of hydrogen-rich compounds has attracted a great deal of attention owing to its interesting structural changes triggered by the relative orientations of adjacent ammonium ions. Previous studies of ammonium iodide have remained in the low pressure range experimentally, which we first extended to so high pressure (250 GPa). We have investigated the structures of ammonium iodine under high pressure through <jats:italic>ab initio</jats:italic> evolutionary algorithm and total energy calculations based on density functional theory. The static enthalpy calculations show that phase V is stable until 85 GPa where a new phase <jats:italic>Ibam</jats:italic> is identified. Calculations of phonon spectra show that the <jats:italic>Ibam</jats:italic> phase is stable between 85 GPa and 101 GPa and the <jats:italic>Cm</jats:italic> phase is stable up to 130 GPa. In addition, ammonium iodine dissociates into NH<jats:sub>3</jats:sub>, H<jats:sub>2</jats:sub>, and I<jats:sub>2</jats:sub> at 74 GPa. Subsequently, we analyzed phonon spectra and electronic band structures, finding that phonon softening is not the reason of dissociation and NH<jats:sub>4</jats:sub>I is always a semiconductor within the pressure range.</jats:p>

<jats:p>We theoretically investigated the properties of the high-order harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized (BCCP) laser field. The harmonic emission processes have been illustrated by numerically solving the two-dimensional time-dependent Schrödinger equation of an atom in intense laser fields. It is found that with the decrease of the right-circularly polarized laser wavelength, the harmonic spectra are gradually splitting and the harmonic orders move towards the higher frequency. Meanwhile, the integer and semi-integer harmonic emission will be generated when the frequency ratios of right- and left-circularly polarized lasers are semi-integer. The emission mechanism of the semi-integer-order harmonics has been investigated by using the rules of photon absorption and emission.</jats:p>

<jats:p>A single-order diffraction transmission grating named spectroscopic photon sieve (SPS) for soft x-ray region is proposed and demonstrated in this paper. The SPS consists of many circular pinholes located randomly, and can realize both free-standing diffractions and the suppression of higher-order differations. In this paper, the basic concept, numerical simulations, and calibration results of a 1000-lines/mm SPS for soft x-ray synchrotron radiation are presented. As predicted by theoretical calculations, the calibration results of a 1000-lines/mm SPS verify that the higher-order diffractions can be significantly suppressed along the symmetry axis. With the current nanofabrication technique, the SPS can potentially have a higher line density, and can be widely used in synchrotron radiation, laser-induced plasma diagnostics, and astrophysics.</jats:p>

<jats:p>We theoretically and numerically study the propagation dynamics of a Gaussian beam modeled by the fractional Schrödinger equation with different dynamic linear potentials. For the limited case <jats:italic>α</jats:italic> = 1 (<jats:italic>α</jats:italic> is the Lévy index) in the momentum space, the beam suffers a frequency shift which depends on the applied longitudinal modulation and the involved chirp. While in the real space, by precisely controlling the linear chirp, the beam will exhibit two different evolution characteristics: one is the zigzag trajectory propagation induced by multi-reflection occurring at the zeros of spatial spectrum, the other is diffraction-free propagation. Numerical simulations are in full accordance with the theoretical results. Increase of the Lévy index not only results in the drift of those turning points along the transverse direction, but also leads to the delocalization of the Gaussian beam.</jats:p>

<jats:p>We simulate pulse shaping of bright–dark vector soliton pair in an optical fiber system. Through changing input pulse parameters (amplitude ratio, projection angle, time delay, and phase difference), different kinds of pulse shapes and spectra can be generated. For input bright–dark vector soliton pair with the same central wavelength, “2+1”- and “2+2”-type pseudo-high-order bright–dark vector soliton pairs are achieved. While for the case of different central wavelengths, bright–dark vector soliton pairs with multiple pulse peaks/dips are demonstrated with appropriate pulse parameter setting.</jats:p>