Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The phase of cross-correlation function of two different normal modes contains source range information, which can be extracted by warping transform due to the dispersive characteristics of the shallow water waveguide. The autocorrelation function of the received pressure or particle velocity contains both modal autocorrelation component (MAC) and modal cross-correlation component (MCC), with the former part usually treated as interference for source ranging. Because the real part of the vertical intensity flux (RPVIF) only contains MCC, a passive impulsive source ranging method based on the frequency warping transform of RPVIF with a single vector receiver in shallow water is presented. Using a waveguide-invariant-based frequency warping operator, the cross-correlation components of two different modes in the vertical intensity flux are warped into separable impulsive sequences, the time delays of which are subsequently used for source ranging. The advantages of source ranging based on warping the vertical intensity flux compared with warping the pressure autocorrelation function are pointed out, and the experiment results are also presented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A novel multi-cavity Helmholtz muffler is proposed. The multi-cavity Helmholtz muffler is composed of steel structures and silicone membranes. With suitable construction, the Helmholtz muffler can be designed to exhibit negative mass density in low frequency, and the muffling frequency can be adjusted when we change the internal structure of the cavity, which will be very attractive for noise control. In this paper, we investigate the influence of the membranes and the cavities on noise reduction characteristics with theoretical calculations and simulations. The results show that the numbers of membranes and the volumes of the cavities can have a great effect on the position of the muffling frequency. The number of cavities can have a great effect on the width of the muffling frequency (reduce the noise by 10 dB). With different combinations of the membranes and cavities, we can get different muffling frequencies, which can meet different muffling demands in practical applications and is more flexible than the traditional Helmholtz cavity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson (GW) model and the Majumdar (MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection (TR) method is introduced into the verification of contact models. An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity’s merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the Fourier–Chebyshev spectral method, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with direct numerical simulation (DNS) methods for different Reynolds numbers. A formula is derived to express the relation between fluctuating velocities and the friction drag coefficient. With the application of electromagnetic force, the in-depth relations among the fluctuating velocities near the wall, Reynolds stress, and the effect of drag reduction for different Reynolds numbers are discussed. The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers. The fluctuating velocities along the streamwise and normal directions are suppressed significantly, while the fluctuating velocity along the spanwise direction is enhanced dramatically due to the spanwise electromagnetic force. However, the values of Reynolds stress depend on the fluctuating velocities along the streamwise and normal directions rather than that along the spanwise direction. Therefore, the significant effect of drag reduction is obtained. Moreover, the maximum drag reduction is weakened due to the decay of control effect for fluctuating velocities as the Reynolds number increases.</jats:p>

<jats:p>A concise theoretical framework, the partial Gauss–Hermite quadrature (pGHQ), is established to construct on-node lattices of the lattice Boltzmann (LB) method under a Cartesian coordinate system. Compared with the existing approaches, the pGHQ scheme has the following advantages: extremely concise algorithm, unifies the constructing procedure for symmetric and asymmetric on-node lattices, and covers a full-range quadrature degree of a given discrete velocity set. We employ the pGHQ scheme to search the local optimal and asymmetric lattices for <jats:inline-formula> <jats:tex-math><?CDATA $\left\{n=3,4,5,6,7\right\}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="}" open="{"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:mo>,</mml:mo> <mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:mn>5</mml:mn> <mml:mo>,</mml:mo> <mml:mn>6</mml:mn> <mml:mo>,</mml:mo> <mml:mn>7</mml:mn> </mml:mrow> </mml:mfenced> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_054702ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> moment degree equilibrium distribution discretization on the range <jats:inline-formula> <jats:tex-math><?CDATA $\left[-10,10\right]$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>10</mml:mn> <mml:mo>,</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:mfenced> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_054702ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The search reveals a surprising abundance of available lattices. Through a brief analysis, the discrete velocity set shows a significant influence on the positivity of equilibrium distributions, which is considered as one of the major impacts of the numerical stability of the LB method. Hence, the results of the pGHQ scheme lay a foundation for further investigations to improve the numerical stability of the LB method by modifying the discrete velocity set. It is also worth noting that pGHQ can be extended into the entropic LB model, even though it was proposed for the Hermite polynomial expansion LB theory.</jats:p>

<jats:p>The particle structure of a complex system has been explored through a unique Evans's homogenous nonequilibrium molecular dynamics (HNEMD) simulation technique. The crystalline order–disorder structures (OD-structures) and the corresponding energies of three-dimensional (3D) nonideal complex systems (NICSs) have been measured over a wide range of plasma states (Γ, <jats:italic>κ</jats:italic>) for a body-centered cubic (BCC) structure. The projected technique provides accurate OD-structures with fast convergence and applicable to very small size effect for different temperatures (<jats:inline-formula> <jats:tex-math><?CDATA $\equiv $?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>≡</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_055201ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> 1 / <jats:inline-formula> <jats:tex-math><?CDATA ${\rm{\Gamma }})$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_055201ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and constant force field (<jats:inline-formula> <jats:tex-math><?CDATA ${F}^{* })$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_055201ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> values. The OD-structure obtained through HNEMD approach is found to be reasonable agreement and more reliable than those earlier identified by simulation approaches and experimental data of NICSs. New simulations of OD-structures show that dusty plasma remains in crystalline (strongly coupled) state at lower temperature and constant <jats:inline-formula> <jats:tex-math><?CDATA ${F}^{* }$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_055201ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> values, for the whole simulation runs. Our investigations show that the crystalline structure is changed and the particle structure switches from intermediate to disorder (nonideal gaseous) state with an increase of the system's temperature. It has been shown that the long range order shifts toward lower temperature with increasing *<jats:inline-formula> <jats:tex-math><?CDATA $\kappa $?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>κ</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_055201ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>. The presented technique exhibits that the potential energy has a maximum value when the dusty plasma remains in crystalline states (low temperatures), which confirms earlier 3D simulation results.</jats:p>

<jats:p>An air-spark switch plasma was diagnosed by the Mach–Zehnder laser interferometer with ultra-high spatial and temporal resolution. The interferograms containing plasma phase shift information at different time were obtained. The phase shift distributions of the plasma were extracted by numerically processing the interferograms. The three-dimensional (3D) electron density distributions of the air-spark switch plasma were then obtained. The working process of the air-spark switch was described by analyzing the temporal and spatial evolution of the plasma electron density.</jats:p>

<jats:p>We have systematically studied the structures, electronic properties, and lattice dynamics of B–P compounds at high pressures. BP and B<jats:sub>6</jats:sub>P are found to be thermodynamically stable below 100 GPa, and other stoichiometries are decomposable under pressure. The predicted structures of <jats:italic>F</jats:italic>-43<jats:italic>m</jats:italic> BP and <jats:italic>R</jats:italic>-3<jats:italic>m</jats:italic> B<jats:sub>6</jats:sub>P are in good agreement with the experimental results by comparing the powder diffraction file (PDF) standard cards with our simulated x-ray diffractions. The bonding properties of BP and B<jats:sub>6</jats:sub>P have also been analyzed by electronic localization functions, charge density difference, and Bader charge analysis. Our results show that BP and B<jats:sub>6</jats:sub>P decompose into B and P under high pressure, which is proven to be dominated by the volumes of them. Furthermore, the infrared and Raman spectra of <jats:italic>F</jats:italic>-43<jats:italic>m</jats:italic> and <jats:italic>R</jats:italic>-3<jats:italic>m</jats:italic> are investigated at selected pressures and will provide useful information for future experimental studies about B–P compounds.</jats:p>

<jats:p>The crystallographic and magnetic properties are presented for van der Waals antiferromagnetic FePS<jats:sub>3</jats:sub>. High-quality single crystals of millimeter size have been successfully synthesized through the chemical vapor transport method. The layered structure and cleavability of the compound are apparent, which are beneficial for a potential exploration of the interesting low dimensional magnetism, as well as for incorporation of FePS<jats:sub>3</jats:sub> into van der Waals heterostructures. For the sake of completeness, we have measured both direct current (dc) and alternating current (ac) magnetic susceptibility. The paramagnetic to antiferromagnetic transition occurs at approximately <jats:inline-formula> <jats:tex-math><?CDATA ${T}_{{\rm{N}}}\sim 115\,{\rm{K}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>115</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">K</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_056102ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The effective moment is larger than the spin-only effective moment, suggesting that an orbital contribution to the total angular momentum of the Fe<jats:sup>2+</jats:sup> could be present. The ac susceptibility is independent of frequency, which means that the spin freezing effect is excluded. Strong anisotropy of out-of-plane and in-plane susceptibility has been shown, demonstrating the Ising-type magnetic order in FePS<jats:sub>3</jats:sub> system.</jats:p>

<jats:p>A new low temperature <jats:italic>Pmmm</jats:italic> (120 K) phase was found in high temperature superconductor Sr<jats:sub>2</jats:sub>CuO<jats:sub>3+<jats:italic>δ</jats:italic> </jats:sub>, which was indicated as a pure electronic phase by resonant x-ray diffraction at Cu <jats:italic>K</jats:italic>-edge. As shown by x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) at Cu <jats:italic>K</jats:italic>-edge, the strong charge density redistribution and local lattice fluctuations around Cu site at the onset of phase transition were due to the occurrence of superconductive coherence, the redistribution and fluctuation finished at <jats:italic>T</jats:italic> <jats:sub>c</jats:sub>. Finally, the electron–lattice interaction was mainly elaborated to understand the superconductivity of Sr<jats:sub>2</jats:sub>CuO<jats:sub>3+<jats:italic>δ</jats:italic> </jats:sub>.</jats:p>