Catálogo de publicaciones - revistas

<jats:p>Radiative heat flux at wall boundaries is important for its thermal design. Numerical methods based on structured grids are becoming trendy due to their simplicity and efficiency. Existing radiative transfer equation solvers produce oscillating radiative heat flux at the irregular boundary if they are based on structured grids. Reverse Monte Carlo method and analytical discrete ordinates method are adopted to calculate the radiative heat flux at complex boundaries. The results show that the reverse Monte Carlo method can generate a smooth radiative heat flux profile and it is smoother with larger energy bundles. The results from the analytical discrete ordinates method show that the fluctuations are due to the ray effect. For the total or the mean radiative heat flux, the results from the analytical discrete ordinates method are very close to those from the reverse Monte Carlo method.</jats:p>

<jats:p>Thermal rectification is a promising way to manipulate the heat flow, in which thermal phonons are spectrally and collectively controlled. As phononic devices are mostly relying on monochromatic phonons, in this work we propose a phononic rectifier based on the carbon schwarzite host–guest system. By using molecular dynamic simulations, we demonstrate that the phononic rectification only happens at a specific frequency of the hybridized mode for the host–guest system, due to its strong confinement effect. Moreover, a significant rectification efficiency, ∼ 134 %, is observed, which is larger than most of the previously observed efficiencies. The study of length and temperature effects on the phononic rectification shows that the monochromaticity and frequency of the rectified thermal phonons depend on the intrinsic anharmonicity of the host–guest system and that the on-center rattling configuration with weak anharmonicity is preferable. Our study provides a new perspective on the rectification of thermal phonons, which would be important for controlling monochromatic thermal phonons in phononic devices.</jats:p>

<jats:p>The quantum hydrodynamic model for ion-acoustic waves in plasmas is studied. First, we design a new disturbance expansion to describe the ion fluid velocity and electric field potential. It should be emphasized that the piecewise function perturbation form is new with great difference from the previous perturbation. Then, based on the piecewise function perturbation, a (3+1)-dimensional generalized modified Korteweg–de Vries Zakharov–Kuznetsov (mKdV-ZK) equation is derived for the first time, which is an extended form of the classical mKdV equation and the ZK equation. The (3+1)-dimensional generalized time-space fractional mKdV-ZK equation is constructed using the semi-inverse method and the fractional variational principle. Obviously, it is more accurate to depict some complex plasma processes and phenomena. Further, the conservation laws of the generalized time-space fractional mKdV-ZK equation are discussed. Finally, using the multi-exponential function method, the non-resonant multiwave solutions are constructed, and the characteristics of ion-acoustic waves are well described.</jats:p>

<jats:p>The classical Navier–Stokes equation (NSE) is the fundamental partial differential equation that describes the flow of fluids, but in certain cases, like high local density and temperature gradient, it is inconsistent with the experimental results. Some extended Navier–Stokes equations with diffusion terms taken into consideration have been proposed. However, a consensus conclusion on the specific expression of the additional diffusion term has not been reached in the academic circle. The models adopt the form of the generalized Newtonian constitutive relation by substituting the convection velocity with a new term, or by using some analogy. In this study, a new constitutive relation for momentum transport and a momentum balance equation are obtained based on the molecular kinetic theory. The new constitutive relation preserves the symmetry of the deviation stress, and the momentum balance equation satisfies Galilean invariance. The results show that for Poiseuille flow in a circular micro-tube, self-diffusion in micro-flow needs considering even if the local density gradient is very low.</jats:p>

<jats:p>Considering that the fluid is inviscid and incompressible and the flow is irrotational in a fixed frame of reference and using the multiple scale analysis method, we derive a nonlinear Schrödinger equation (NLSE) describing the evolution dynamics of gravity-capillary wavetrains in arbitrary constant depth. The gravity-capillary waves (GCWs) are influenced by a linear shear flow (LSF) which consists of a uniform flow and a shear flow with constant vorticity. The modulational instability (MI) of GCWs with the LSF is analyzed using the NLSE. The MI is effectively modified by the LSF. In infinite depth, there are four asymptotes which are the boundaries between MI and modulational stability (MS) in the instability diagram. In addition, the dimensionless free surface elevation as a function of time for different dimensionless water depth, surface tension, uniform flow and vorticity is exhibited. It is found that the decay of free surface elevation and the steepness of free surface amplitude change over time, which are greatly affected by the water depth, surface tension, uniform flow and vorticity.</jats:p>

<jats:p>Measuring walking forces of small or tiny insects can help the comprehension of their locomotion principles. However, as their size and force are generally too small, walking forces of small insects in sub-mg mass have never been actually measured. In this work, a convenient multi-lens and jelly surface based shadow method was developed for simultaneous multiple walking forces measuring, ranged from nN to mN with a sensitivity of sub-nN/pixel under ambient conditions. Walking force of six legs of a 0.3 mg water treader was demonstrated. The obtained results disclosed a rapid and extending middle leg strategy of water treader in walking forward above a jelly surface. This method is cost-effective and high-resolution, which could be easily used in measuring other tiny forces.</jats:p>

<jats:p>The non-spherical lowest-lying Li<jats:sub> <jats:italic>n</jats:italic> </jats:sub> (<jats:italic>n</jats:italic> = 15–17) isomers were found with high symmetric compact structures, of which the stability was not rationalized in a previous report (<jats:italic>J. Chem. Phys.</jats:italic> <jats:bold>119</jats:bold> 9444 (2003)). Based on the newly proposed super-valence bond model, the three prolate lithium clusters can be viewed as magnetic superatomic molecules, which are composed by sharing valence electron pairs and nuclei between two superatom units, namely, Li<jats:sub>10</jats:sub> or Li<jats:sub>11</jats:sub>, and thus their stability can be given a good understanding. Molecular orbital and chemical bonding analysis clearly reveal that the Li<jats:sub> <jats:italic>n</jats:italic> </jats:sub> (<jats:italic>n</jats:italic> = 15–17) clusters with prolate shapes are magnetic superatomic molecules. Our work may aid in the developments of the cluster-assembled materials or superatom-bonds.</jats:p>

<jats:p>We investigate characteristics of multi-arc torches with three pairs of electrodes (three cathodes and three anodes) and their performance on the spheroidization of SiO<jats:sub>2</jats:sub> powder. The effect of electrode arrangement, including adjacent pattern (AD pattern, adjacent electrodes powered by one power supply) and opposite pattern (OP pattern, opposite electrodes powered by one power supply), on the dynamics of arc plasma is investigated based on synchronous acquisition of electrical and optical signals. The results show that both the voltage and spatial distribution of each arc of multiple arcs are more stable compared with those of a single arc. The fluctuation of an arc in multiple arcs mainly comes from the small-scale arc-to-arc restrikes among multiple arcs. Moreover, these arc-to-arc restrikes occur more frequently among multiple arc columns in OP pattern than in AD pattern. Moreover, the high-temperature area of the central region of arc chamber in OP pattern is larger than that in AP pattern. For the spheroidization of SiO<jats:sub>2</jats:sub> in this multi-arc generator, the spheronization degrees of plasma treated silica in OP pattern are at least 20% higher than those in AD pattern.</jats:p>

<jats:p>We introduce a new class of the chirped Airy–Gaussian vortex electron plasma (CAiGVEP) wave which constitutes the exact and continuous transition modes between the chirped Airy vortex and the chirped Gaussian vortex electron plasma wave. The intensity, the phase, and the angular momentum density flow of the CAiGVEP wave are discussed under different distribution factors and different chirp modes.</jats:p>

<jats:p>TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800 °C can limit their further high-temperature structural applications. To improve the oxidation resistance of a high-Nb-content <jats:italic>γ</jats:italic>-TiAl alloy (Ti-45Al-8.5Nb, in units of at.%), a chromium (Cr) coating is prepared by using the plasma surface alloying technique, separately, at 800 °C and 1000 °C. The x-ray diffraction (XRD) patterns reveal that an oxide surface layer consisting of Cr<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>, Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>, and TiO<jats:sub>2</jats:sub> is produced on the Cr-coated Nb containing <jats:italic>γ</jats:italic>-TiAl substrates during the initial oxidation. However, the Cr<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage (≤ 90 h) and a biquadratic law stage (≥ 90 h), fit by weight–gain curves. Due to diffusion in the fabrication process and oxidation process, the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45Al-8.5Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.</jats:p>