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<jats:p>The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article. Collimators are used to achieve the desired vapor beam and deposition rate profile in some applications. This increases the difficulty measuring boundary conditions and the size of the liquid metal pool inside the collimators. It is accordingly hard to obtain accurate results from numerical calculations. In this article, two-dimensional direct simulation Monte Carlo (DSMC) codes are executed to quantify the influence of uncertainties of boundary conditions and pool sizes. Then, three-dimensional DSMC simulations are established to simulate cerium and neodymium evaporation with the collimator. Experimental and computational results of substrate deposition rate profile are in excellent agreement at various evaporation rates and substrate heights. The results show that the DSMC method can assist in metal evaporation with a collimator.</jats:p>

<jats:p>Flight feathers stand out with extraordinary mechanical properties for flight because they are lightweight but stiff enough. Their elasticity has great effects on the aerodynamics, resulting in aeroelasticity. Our primary task is to figure out the stiffness distribution of the feather to study the aeroelastic effects. The feather shaft is simplified as a beam, and the flexibility matrix of an eagle flight feather is tested. A numerical method is proposed to estimate the stiffness distributions along the shaft length based on an optimal Broyden–Fletcher–Goldfarb–Shanno (BFGS) method with global convergence. An analysis of the compressive behavior of the shaft based on the beam model shows a good fit with experimental results. The stiffness distribution of the shaft is finally presented using a 5th order polynomial.</jats:p>

<jats:p>The coupled effect of wall heat loss and viscosity friction on flame propagation and deflagration to detonation transition (DDT) in micro-scale channel is investigated by high-resolution numerical simulations. The results show that when the heat loss at walls is considered, the oscillating flame presents a reciprocating motion of the flame front. The channel width and Boit number are varied to understand the effect of heat loss on the oscillating flame and DDT. It is found that the oscillating propagation is determined by the competition between wall heat loss and viscous friction. The flame retreat is led by the adverse pressure gradient caused by thermal contraction, while it is inhibited by the viscous effects of wall friction and flame boundary layer. The adverse pressure gradient formed in front of a flame, caused by the heat loss and thermal contraction, is the main reason for the flame retreat. Furthermore, the oscillating flame can develop to a detonation due to the pressure rise by thermal expansion and wall friction. The transition to detonation depends non-monotonically on the channel width.</jats:p>

<jats:p>Radiation from laser-produced plasmas was examined as a potential wavelength calibration source for spectrographs in the extreme ultraviolet (EUV) region. Specifically, the EUV emission of chromium (Cr) plasmas was acquired via spatio-temporally resolved emission spectroscopy. With the aid of Cowan and flexible atomic code (FAC) structure calculations, and a comparative analysis with the simulated spectra, emission peaks in the 6.5–15.0 nm range were identified as 3p–4d, 5d and 3p–4s transition lines from Cr<jats:sup>5+</jats:sup>–Cr<jats:sup>10+</jats:sup> ions. A normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model were assumed for the spectral simulations, and used to estimate the electron temperature and density in the plasma. The results indicate that several relatively isolated emission lines of highly charged ions would be useful for EUV wavelength calibration.</jats:p>

<jats:p>During a dc corona discharge, the ions’ momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind. The characteristics of corona discharge and the induced ionic wind are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration. The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode. Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage. The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition. The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model. The ionic wind of negative corona is mainly affected by negative ions. The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area. The ionic wind of positive corona is mainly affected by positive ions. The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.</jats:p>

<jats:p>It is generally accepted that during collisionless magnetic reconnection, electrons flow toward the X line in the separatrix region, and then an electron depletion layer is formed. In this paper, with two-dimensional (2D) particle-in-cell (PIC) simulation, we investigate the characteristics of the separatrix region during magnetic reconnection. In addition to the electron depletion layer, we find that there still exists an electric field parallel to the magnetic field in the separatrix region. Because a reduced ion-to-electron mass ratio and light speed are usually used in PIC simulation models, we also change these parameters to analyze the characteristics of the separatrix region. It is found that the increase in the ion-to-electron mass ratio makes the electron depletion layer and the parallel electric field more obvious, while the influence of light speed is less pronounced.</jats:p>

<jats:p>The influence of vibration on the spatiotemporal structure of the pattern in dielectric barrier discharge is studied for the first time. The spatiotemporal structure of the pattern investigated by an intensified charge-coupled device shows that it is an interleaving of three sublattices, whose discharge sequence is small rods–halos–large spots in each half-cycle of the applied voltage. The result of the photomultiplier indicates that the small rods are composed of moving filaments. The moving mode of the moving filaments is determined to be antisymmetric stretching vibration by analyzing a series of consecutive images taken by a high-speed video camera. The antisymmetric stretching vibration affects the distribution of wall charges and leads to the halos. Furthermore, large spots are discharged only at the centers of the squares consisting of vibrating filaments. The vibration mechanism of the vibrating filaments is dependent on the electric field of wall charges.</jats:p>

<jats:p>Films of poly(9,9-dioctylfluorene) (PFO) are of great importance in fabricating light emitting diodes. In practice, the (<jats:italic>β</jats:italic>-phase of PFO is expected due to its high efficiency in the transport of charge carrier. To promote the formation of (<jats:italic>β</jats:italic>-phase, PFO films are immersed and annealed in the mixture of solvent/nonsolvent. The effects of temperature, solvent/nonsolvent ratio, and annealing time are examined systematically. It is found that the fraction of (<jats:italic>β</jats:italic>-phase can be highly improved by increasing the ratio of solvent/nonsolvent. The reconfiguration of PFO molecules for (<jats:italic>β</jats:italic>-phase in annealing is generally finished in 10 min. The finding in this study demonstrates that solvent-assisted annealing offers a fast and economic approach for mass annealing.</jats:p>

<jats:p>By combining temperature-dependent x-ray diffraction (XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic–inorganic perovskite CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub>. The XRD measurements cover distinct phases between 15 K and 370 K and demonstrate a general positive thermal expansion. Clear anomalies are found around the transition temperatures. The temperature evolution of the lattice constants reveals that the transition at 160 K/330 K is of the first-/second-order type. Raman measurements uncover three strong low-frequency modes, which can be ascribed to the vibration of the Pb/I atoms. The temperature evolution of the modes clearly catches these transitions at 160 K and 330 K, and confirms the transition types, which are exactly consistent with the XRD results. The present study may set an experimental basis to understand the high conversion efficiency in methylammonium lead iodide.</jats:p>

<jats:p>Micron-sized diamond particles containing germanium-vacancy (Ge-V) color centers with a zero-photon line (ZPL) around 602.3 nm are successfully grown using hot filament chemical vapor deposition. The crystal morphology changes from icosahedron to truncated octahedron and decahedron, finally becomes spherical with the growth pressure increase. Due to the chamber containing Si, all diamond particles contain silicon-vacancy (Si-V) color centers. High growth pressure contributes to the formation of Ge-V and Si-V in diamonds. With prolonging growth time, the change in the full width at half maximum (FWHM) of the diamond peak is small, which shows that the concentration of Ge-V and Si-V centers nearly maintains a constant. The FWHM of the Ge-V ZPL is around 4 nm, which is smaller than that reported, suggesting that the Ge-V center has a more perfect structure. Ge-V and Si-V photoluminescence (PL) intensities increase with the prolonging growth time due to the increased diamond content and reduced content of sp<jats:sup>2</jats:sup>-bonded carbon and trans-polyacetylene. In summary, increasing the growth pressure and prolonging the growth time are beneficial to enhance the Ge-V and Si-V PL intensities.</jats:p>