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<jats:p>In the biological locomotion, the ambit pressure is of particular importance to use as a means of propulsion. The multiple vortex rings have been proved to generate additional thrust by interaction, but the mechanism of this thrust enhancement is still unknown. This study examines the effect of ambit pressure on formation enhancement in interacting dual vortex rings. The vortex rings, which have the same formation time, are successively generated in a piston-cylinder apparatus. The finite-time Lyapunov exponent (FTLE) visualizes the flow fields as an indication of Lagrangian coherent structures (LCSs), and the pressure field is calculated based on the digital particle image velocity (DPIV). We extract the back pressure of the rear vortex in dual vortices and the back pressure circulation <jats:italic>Γ</jats:italic> <jats:sub>b</jats:sub>, which is defined as a form of overpressure circulation <jats:italic>Γ</jats:italic> <jats:sub>p</jats:sub>. The <jats:italic>Γ</jats:italic> <jats:sub>b</jats:sub> has a positive linear relationship with <jats:italic>Γ</jats:italic> <jats:sub>p</jats:sub>. A critical interval distance <jats:inline-formula> <jats:tex-math> <?CDATA ${d}_{{\rm{cr}}}^{* }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>d</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">cr</mml:mi> </mml:mrow> <mml:mo>*</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_8_084701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in a range of 0.32–0.42 is found where <jats:italic>Γ</jats:italic> <jats:sub>b</jats:sub> and <jats:italic>Γ</jats:italic> <jats:sub>p</jats:sub> reach the maximum synchronously, leading to a full-interaction mode. Moreover, an over-interaction mode and an under-interaction mode are proposed when the dimensionless interval distance <jats:italic>d</jats:italic>* is smaller or larger than <jats:inline-formula> <jats:tex-math> <?CDATA ${d}_{{\rm{cr}}}^{* }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>d</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">cr</mml:mi> </mml:mrow> <mml:mo>*</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_8_084701_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. To conclude, the high back pressure caused by vortex interaction can enhance the formation of vortex rings and lead to high thrust.</jats:p>

<jats:p>This research presents the applications of entropy generation phenomenon in incompressible flow of Jeffrey nanofluid in the presence of distinct thermal features. The novel aspects of various features, such as Joule heating, porous medium, dissipation features, and radiative mechanism are addressed. In order to improve thermal transportation systems based on nanomaterials, convective boundary conditions are introduced. The thermal viscoelastic nanofluid model is expressed in terms of differential equations. The problem is presented via nonlinear differential equations for which analytical expressions are obtained by using the homotopy analysis method (HAM). The accuracy of solution is ensured. The effective outcomes of all physical parameters associated with the flow model are carefully examined and underlined through various curves. The observations summarized from current analysis reveal that the presence of a permeability parameter offers resistance to the flow. A monotonic decrement in local Nusselt number is noted with Hartmann number and Prandtl number. Moreover, entropy generation and Bejan number increases with radiation parameter and fluid parameter.</jats:p>

<jats:p>A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated. Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the laser. More atoms in the brass sample are excited. As a secondary excitation source, spark discharge reheats the generated plasma, which further amplifies the enhancement results of nanoparticles. The spectral intensity with the spark discharge increases more obviously with nanoparticle concentration increasing than without the spark discharge. Also, plasma temperature and electron density are calculated by the Boltzmann plot and Stark broadening. The changes in the plasma temperature and electron density are consistent with the spectral emission changes.</jats:p>

<jats:p>Two classic radio-frequency (RF) plasmas, i.e., the capacitively and the inductively coupled plasmas (CCP and ICP), are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures (mTorr–Torr), high-frequency electric field (13.56 MHz–200 MHz), reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas, and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.</jats:p>

<jats:p>The Ammann–Beenker tiling is a typical model for two-dimensional octagonal quasicrystals. The geometric properties of local configurations are the key to understanding its formation mechanism. We study the configuration correlations in the framework of Ammann lines, giving an in-depth inspection of this eightfold symmetric structure. When both the vertex type and the orientation are taken into account, strict confinements of neighboring vertices are found. These correlations reveal the structural properties of the quasilattice and also provide substitution rules of vertex along an Ammann line.</jats:p>

<jats:p>Space radiation with inherently broadband spectral flux poses a huge danger to astronauts and electronics on aircraft, but it is hard to simulate such feature with conventional radiation sources. Using a tabletop laser-plasma accelerator, we can reproduce exponential energy particle beams as similar as possible to these in space radiation. We used such an electron beam to study the electron radiation effects on the surface structure and performance of two-dimensional material (FePS<jats:sub>3</jats:sub>). Energetic electron beam led to bulk sample cleavage and damage between areas of uneven thickness. For the FePS<jats:sub>3</jats:sub> sheet sample, electron radiation transformed it from crystalline state to amorphous state, causing the sample surface to rough. The full widths at the half maximum of characteristic Raman peaks became larger, and the intensities of characteristic Raman peaks became weak or even disappeared dramatically under electron radiation. This trend became more obvious for thinner samples, and this phenomenon was attributed to the cleavage of P–P and P–S bonds, destabilizing the bipyramid structure of [P<jats:sub>2</jats:sub>S<jats:sub>6</jats:sub>]<jats:sup>4–</jats:sup> unit. The results are of great significance for testing the maximum allowable radiation dose for the two-dimensional material, implying that FePS<jats:sub>3</jats:sub> cannot withstand such energetic electron radiation without an essential shield.</jats:p>

<jats:p>The core structure, Peierls stress and core energy, etc. are comprehensively investigated for the 90° dislocation and the 60° dislocation in metal aluminum using the fully discrete Peierls model, and in particular thermal effects are included for temperature range 0 ≤ <jats:italic>T</jats:italic> ≤ 900 K. For the 90° dislocation, the core clearly dissociates into two partial dislocations with the separating distance <jats:italic>D</jats:italic> ∼ 12 Å, and the Peierls stress is very small <jats:italic>σ</jats:italic> <jats:sub>p</jats:sub> &lt; 1 kPa. The nearly vanishing Peierls stress results from the large characteristic width and a small step length of the 90° dislocation. The 60° dislocation dissociates into 30° and 90° partial dislocations with the separating distance <jats:italic>D</jats:italic> ∼ 11 Å. The Peierls stress of the 60° dislocation grows up from 1 MPa to 2 MPa as the temperature increases from 0 K to 900 K. Temperature influence on the core structures is weak for both the 90° dislocation and the 60° dislocation. The core structures theoretically predicted at <jats:italic>T</jats:italic> = 0 K are also confirmed by the first principle simulations.</jats:p>

<jats:p>High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted. In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 kW is used to drive the gas thermal blooming, and a 50-mW high-beam-quality 637-nm laser diode (LD) is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results.</jats:p>

<jats:p>We investigate the angular dependence of proton-induced single event transient (SET) in silicon-germanium heterojunction bipolar transistors. Experimental results show that the overall SET cross section is almost independent of proton incident angle. However, the proportion of SET events with long duration and high integral charge collection grows significantly with the increasing angle. Monte Carlo simulations demonstrate that the integral cross section of proton incident events with high ionizing energy deposition in the sensitive volume tends to be higher at larger incident angles, which is associated with the angular distribution of proton-induced secondary particles and the geometry of sensitive volume.</jats:p>

<jats:p>Two-dimensional materials have a wide range of applications in many aspects due to their unique properties. Here we carry out a detailed structural search and design of the BP<jats:sub>2</jats:sub> using the first principles method, and find a new PMM2 sheet. The analysis of the phonon dispersive curves shows that the 2D PMM2 is dynamic stable. The study of molecular dynamics shows that the 2D PMM2 can be stable under high temperature, even at 600 K. Most importantly, when a suitable strain is applied, the structure can exhibit other electronic properties such as direct band gap semiconductor. In addition, the small strain can tune the band gap value of the PMM2 structure to around 1.4 eV, which is very close to the ideal band gap of solar materials. Therefore, the 2D PMM2 may have potential applications in the field of photovoltaic materials.</jats:p>