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<jats:p>A complex system contains generally many elements that are networked by their couplings. The time series of output records of the system’s dynamical process is subsequently a cooperative result of the couplings. Discovering the coupling structure stored in the time series is an essential task in time series analysis. However, in the currently used methods for time series analysis the structural information is merged completely by the procedure of statistical average. We propose a concept called mode network to preserve the structural information. Firstly, a time series is decomposed into intrinsic mode functions and residue by means of the empirical mode decomposition solution. The mode functions are employed to represent the contributions from different elements of the system. Each mode function is regarded as a mono-variate time series. All the mode functions form a multivariate time series. Secondly, the co-occurrences between all the mode functions are then used to construct a threshold network (mode network) to display the coupling structure. This method is illustrated by investigating gait time series. It is found that a walk trial can be separated into three stages. In the beginning stage, the residue component dominates the series, which is replaced by the mode function numbered <jats:italic>M</jats:italic> <jats:sub>14</jats:sub> with peaks covering ∼680 strides (∼12 min) in the second stage. In the final stage more and more mode functions join into the backbone. The changes of coupling structure are mainly induced by the co-occurrent strengths of the mode functions numbered as <jats:italic>M</jats:italic> <jats:sub>11</jats:sub>, <jats:italic>M</jats:italic> <jats:sub>12</jats:sub>, <jats:italic>M</jats:italic> <jats:sub>13</jats:sub>, and <jats:italic>M</jats:italic> <jats:sub>14</jats:sub>, with peaks covering 200–700 strides. Hence, the mode network can display the rich and dynamical patterns of the coupling structure. This approach can be extended to investigate other complex systems such as the oil price and the stock market price series.</jats:p>

<jats:p>The celebrated (1+1)-dimensional Korteweg de–Vries (KdV) equation and its (2+1)-dimensional extension, the Kadomtsev–Petviashvili (KP) equation, are two of the most important models in physical science. The KP hierarchy is explicitly written out by means of the linearized operator of the KP equation. A novel (2+1)-dimensional KdV extension, the cKP3–4 equation, is obtained by combining the third member (KP3, the usual KP equation) and the fourth member (KP4) of the KP hierarchy. The integrability of the cKP3–4 equation is guaranteed by the existence of the Lax pair and dual Lax pair. The cKP3–4 system can be bilinearized by using Hirota’s bilinear operators after introducing an additional auxiliary variable. Exact solutions of the cKP3–4 equation possess some peculiar and interesting properties which are not valid for the KP3 and KP4 equations. For instance, the soliton molecules and the missing D–Alembert type solutions (the arbitrary travelling waves moving in one direction with a fixed model dependent velocity) including periodic kink molecules, periodic kink-antikink molecules, few-cycle solitons, and envelope solitons exist for the cKP3–4 equation but not for the separated KP3 equation and the KP4 equation.</jats:p>

<jats:p>We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polaron-transformed Redfield equation combined with full counting statistics. The steady state heat currents are obtained via this unified approach over a wide region of system–bath coupling, and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits, respectively. A giant heat amplification phenomenon emerges in the strong system–bath coupling limit, where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism. Moreover, the heat amplification is also exhibited with moderate coupling strength, which can be properly explained within the polaron framework.</jats:p>

<jats:p>It is very important to determine the phase transition temperature, such as the water/ice coexistence temperature in various water models, via molecular simulations. We show that a single individual direct simulation is sufficient to get the temperature with high accuracy and small computational cost based on the generalized canonical ensemble (GCE). Lennard–Jones fluids, the atomic water models, such as TIP4P/2005, TIP4P/ICE, and the mW water models are applied to illustrate the method. We start from the coexistent system of the two phases with a plane interface, then equilibrate the system under the GCE, which can stabilize the coexistence of the phases, to directly derive the phase transition temperature without sensitive dependence on the applied parameters of the GCE and the size of the simulation systems. The obtained result is in excellent agreement with that in literatures. These features make the GCE approach in determining the phase transition temperature of systems be robust, easy to use, and particularly good at working on computationally expensive systems.</jats:p>

<jats:p>In this paper, we propose a new enhanced GaN MISFET with embedded pn junction, <jats:italic>i.e.</jats:italic>, EJ-MISFET, to enhance the breakdown voltage. The embedded pn junction is used to improve the simulated device electric field distribution between gate and drain, thus achieving an enhanced breakdown voltage (BV). The proposed simulated device with <jats:italic>L</jats:italic> <jats:sub>GD</jats:sub> = 15μm presents an excellent breakdown voltage of 2050 V, which is attributed to the improvement of the device electric field distribution between gate and drain. In addition, the ON-resistance (<jats:italic>R</jats:italic> <jats:sub>ON</jats:sub>) of 15.37 Ω ⋅mm and Baliga’s figure of merit of 2.734 GW⋅cm<jats:sup>−2</jats:sup> are achieved in the optimized EJ-MISFET. Compared with the field plate conventional GaN MISFET (FPC-MISFET) without embedded pn junction structure, the proposed simulated device increases the BV by 32.54% and the Baliga’s figure of merit is enhanced by 71.3%.</jats:p>

<jats:p>In this study, CdS/ZnO (2:3 mol%) thin films are successfully deposited on quartz substrates by using the sputtering technique. Good images on the structural and optical characteristic features of CdS/ZnO thin films before and after annealing are obtained. The CdS/ZnO thin films are annealed respectively at temperatures of 373 K, 473 K, and 573 K and the structural features are examined by XRD, ATR-FTIR, and FESEM. The optical properties of CdS/ZnO thin films such as refractive indices, absorption coefficients, optical band gap energy values, Urbach energy values, lattice dielectric constants, and high frequency dielectric constants are determined from spectrophotometer data recorded over the spectral range of 300 nm–2500 nm. Dispersion parameters are investigated by using a single-oscillator model. Photoluminescence spectra of CdS/ZnO thin films show an overall decrease in their intensity peaks after annealing. The third-order nonlinear optical parameter, and nonlinear refractive index are also estimated.</jats:p>

<jats:p>We investigate high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser pulses by numerically solving the time-dependent Schrödinger equation. It is found that the minimum energy position of the harmonic spectrum and the non-integer order optical radiation are greatly discrepant for different atomic potentials. By analyzing the quantum trajectory of the harmonic emission, discrepancies among the harmonic spectra from different potentials can be attributed to the action of the potential on the ionized electrons. In addition, based on the influence of the driving light intensity on the overall intensity and ellipticity of higher order harmonics, the physical conditions for generating a high-intensity circularly polarized harmonic can be obtained.</jats:p>

<jats:p>As is well known, the basic intrinsic properties of materials can be significant for their practical applications. In this work, the room-temperature absorption, transmittance, reflectance spectra, and relative photoelectricities parameters of the Mg<jats:sub>4</jats:sub>Ta<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> crystals are demonstrated. Meanwhile, the polarized Raman spectra of Mg<jats:sub>4</jats:sub>Ta<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> crystals are also described. The room-temperature photoluminescence (PL) and the temperature-dependent PL for Mg<jats:sub>4</jats:sub>Ta<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> crystals are obtained. Significantly, we observe a phonon-participated PL process in Mg<jats:sub>4</jats:sub>Ta<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub>.</jats:p>

<jats:p>The lattice structures of epitaxial Fe<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub> films deposited on MgO were studied systematically using polarized Raman spectroscopy as a function of film thickness, where interesting phenomena were observed. Firstly, the spectral conflict to the Raman selection rules (RSRs) was observed under cross-sectional configuration, which can be attributed to the tetragonal deformation in the growth direction due to the lattice mismatch between Fe<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub> and MgO. Secondly, the blue shift and broadening of Raman peaks evidenced the decrease of the tensile strain in Fe<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub> films with decreasing thickness. Thirdly, distinct from the other Raman modes, the lowest <jats:italic>T</jats:italic> <jats:sub>2g</jats:sub> mode exhibited asymmetric lineshape, which can be interpreted using the spatial correlation model. The increased correlation length introduced in the model can well explain the enhanced peak asymmetry feature with decreasing thickness. These results provide useful information for understanding the lattice structure of epitaxial Fe<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub> film.</jats:p>

<jats:p>We report an effective method for enhancing the photoassociation of ultracold atoms using a non-resonant magnetic field, which enables the manipulation of the coupling between the wavefunctions of the colliding atomic pairs and the excited molecules. A series of photoassociation spectra are measured for different magnetic fields. We show that the photoassociation rate is significantly dependent on the non-resonant magnetic field. A qualitatively theoretical explanation is provided, and shows a good agreement with the experimental result.</jats:p>