International Journal of Modern Physics B

This paper reports the design of a deformable honeycomb acoustic metamaterial, which consists of honeycomb structures and ethylene-vinyl acetate (EVA) copolymer films stacked on each other. The FEA results agree well with the experiment analysis, and it is proved that the proposed structure can break the acoustic mass law below 1000 Hz. This paper reveals that dislocation, compression, and tensile deformation can regulate the sound transmission loss (STL) in a wider frequency range. It is concluded that the STL of a bilayer structure is, on average, 10 dB higher than that of a monolayer structure at low-frequencies. When the dislocation distance b = 1.5 mm, the corresponding STLs reach their maximum values. The FEA and experiment results prove that compression and tensile deformation can considerably improve the sound insulation effect. Such a deformable honeycomb acoustic metamaterial with high STL provides a new concept for engineering noise control.

In the present study, we have investigated the phonon and thermodynamic properties of bulk zinc-blende CdS by first-principle calculations within the density functional theory (DFT) and the density functional perturbation theory (DFPT) method using the quasi harmonic approximation (QHA). We calculated the phonon dispersion at several high symmetry directions, density of phonon state, temperature dependence feature of Helmholtz free energy (F), internal energy, bulk modulus, constant-volume specific heat, entropy, coefficient of the volume thermal expansion and Grüneisen parameter estimated with the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential and compared them with each other. For internal energy, Helmholtz free energy, constant volume heat capacity and phonon entropy the LDA and GGA results are very similar. But, the LDA gives lattice constants that are smaller than GGA while phonon frequencies, bulk modulus and cohesive energies are larger. On the other hand, the results obtained through the GGA approximation for the coefficient of the volume thermal expansion and Grüneisen parameter are larger than those obtained from LDA.

In this paper, for the first time, a new design for a MEMS cantilever-based energy harvester (EH) has been proposed which takes advantage of two engineered piezoelectric layers. The output voltage of the EH has been increased by the aid of making grooves in the piezoelectric layers. By application of the grooves in the piezoelectric layers, the sensitivity of the cantilever as the vibration sensor or the EH has been improved. Results have shown that these grooves can increase the output voltage and decrease the resonance frequency which are desired changes in designing EHs. The single and double groove bimorph cantilevers have been compared and discussed. The position, length and depth of the grooves have been used as optimization parameters and consequently an optimal design has been proposed at the end of the paper. In the optimal design the top and the bottom piezoelectric layers have not covered the entire beam and have different lengths to produce maximum voltage. By means of groove engineering, we could rise the voltage from 5.395 V to 28.35 V which is considered a great improvement compared to other structures reported previously.

Geometric and electronic structures of W${}_m$Cu${}_n$H₂ (m + n $\le$ 7) clusters have been systematically calculated by density functional theory (DFT) at the generalized gradient approximation (GGA) level for ground-state structures. For all W–Cu clusters, H atoms prefer to attach to W atoms in this system during adsorption. And more electrons transfer from H atom to W atom with the growth of the size of the cluster which benefits the hydrogen storage. Analysis of stability properties and electronic properties shows that hydrogen adsorption and dissociation process take place more efficiently at the W₂Cu₃H₂ cluster than the others. Due to high thermodynamic stability and adsorption energy of W₅CuH₂ cluster among W${}_m$Cu${}_n$H₂ (m + n $\le$ 7) clusters, W₅Cu is more suitable for hydrogen storage.

The band structure of Al${}_x$Ga${}_{1-x}$Sb semiconducting ternary alloys and their related properties such as elastic constants, microhardness, transition pressure to the first phase, acoustic wave velocities and melting temperature have been investigated. The calculations are performed using a pseudopotential approach within the virtual crystal approximation which includes the effect of compositional disorder as an effective potential. Generally, our results are found to be in good accord with the experimental results. The composition dependence of all features of interest showed a monotonic behavior and suggests that the stiffness, hardness and structural stability becomes better in Al${}_x$Ga${}_{1-x}$Sb for higher Al concentrations. The bulk sound speeds and melting temperature are found to become larger when increasing the Al content.

The structural and mechanical properties of 9R diamond and 12R diamond have been investigated by using the first-principles calculations. The elastic constants, bulk modulus and Young’s modulus at various pressures have been investigated. The elastic anisotropy under pressure from 0 to 100 GPa has been studied. From our calculations, we found that 9R diamond and 12R diamond have similar high elastic constants and elastic modulus as lonsdaleite and diamond. The detailed ideal strength calculations show that 9R diamond and 12R diamond are intrinsic superhard materials.

In this paper, we study the static and dynamic properties of vortices formation in a rotating Bose–Einstein condensate in synthetic magnetic field. The condensate is confined in a harmonic potential and an optical lattice potential. We numerically solve the time-dependent Gross–Pitaevskii equation in two dimensions and compare the vortices formation process with rotating frame method. We derive the two expressions about vortex number N${}_{\mathrm{\text{v}}}$ and chemical potential $\mu$ as a function of rotational frequency $\mathrm{\Omega }$, which show that the number of vortices N${}_{\mathrm{\text{v}}}$ increases linearly with $\mathrm{\Omega }$, while the chemical potential $\mu$ remains nearly unchanged with increasing $\mathrm{\Omega }$. The analytical results are in qualitative agreement with the numerical ones. Moreover, we also investigate the vortex dynamics. Numerical results indicate that the time spent for the formation of steady state vortices is reduced drastically if the optical lattice is considered. Nevertheless, the synthetic magnetic field approach is still low efficient to generate more vortices.

Glasses in the 25BaSO${}_4-$30B₂O${}_3-$(45 −x)P₂O${}_5-$xDy₂O₃ system with x = 0.1, 0.3, 0.5, 0.7 and 1.0 mol% have been prepared by the melt quenching approach with the aim of using it for optical and white light application. The structural properties are examined by Fourier transform infrared and Raman spectroscopy. The amorphous state of the glasses matrices is determined by X-ray diffraction. Direct and indirect energy bandgap have been evaluated via the data found from UV–visible–near IR spectroscopy. The spectral absorption, emission and excitation are measured, and it is found that the glass doped Dy₂O₃ ions display good UV-excited luminescence of ⁴F${}_{9/2}{\to }^6$H${}_{15/2}$ and ⁴F${}_{9/2}{\to }^6$H${}_{13/2}$ transition around 480–500 and 570–600 nm corresponding to blue and yellow regions respectively. The physical parameters of the glasses have also been calculated. Infrared and Raman of the borosulfophosphate glasses revealed intense spectrum which is characterized by distinct bands.

Electronic, mechanic and lattice dynamic properties of yttrium-based compounds, X₃Y, where X = Pd, Pt and Rh were investigated using the density functional theory. The electronic band calculations demonstrated that X₃Y compounds are metallic at the cubic crystal structures. The calculated elastic constants using the energy-strain method indicate that the three materials are mechanically stable. The calculated bulk modulus and Young’s modulus values suggest that the Pt₃Y is stiffer than that of the other two. The type of bonding and ductility in the X₃Y compounds were also evaluated based on their B/G ratios, Cauchy pressures (C${}_{12}$–C${}_{44}$) and band structure calculations. These compounds were found to be ductile in nature. The density functional perturbation theory was used to derive full phonon frequencies and total and projected phonon density of states. The computed full phonon spectra for X₃Y compounds show that these compounds in the L1₂ phase are dynamically stable. Debye temperature and specific heat of these compounds were also calculated and evaluated using quasi harmonic approximation.

Two-dimensional (2D) layered materials such as transition-metal dichalcogenides TS${}_{2(1-m)}$X${}_{2m}$ (T = Mo, W; X = Se, Te) are available in mono and bilayers forms. The Rashba spin splitting is induced by the breaking of inversion symmetry in monolayer. The electronic structure of TS${}_{2(1-m)}$X${}_{2m}$ is sensitive to an applied electric field. The perpendicular electric field can tune the energy gap. The semiconductor–metal transition appears under the critical electric field in the MoSSe/WSSe heterobilayer, and MoSTe/WSTe heterobilayer exhibits metal character due to spin–orbit coupling. Moreover, the results show that during sodiation/desodiation processes single-phase transition occurs with one one-dimensional (1D) transportation paths of sodium ions in MoS₂, suggesting fast diffusion. Our results provide important insights into a wide range of applications of spin-polarized semiconductors and energy storage for transition-metal dichalcogenides TS${}_{2(1-m)}$X${}_{2m}$.

An asymmetric quantum well (AQW) system that is pumped by two infrared beams is designed to generate terahertz (THz) waves. The refractive index and phase mismatch associated with the intersubband transition of the AQW structure are calculated and analyzed for both present and absent conduction band nonparabolicity. The calculated results reveal that, for increasing wavelengths, the refractive index of the AQW for the short-wavelength pump beam varies more than 0.83 and undergoes a 0.204 $\mu$m redshift, when the conduction band nonparabolicity is considered. The variation of the refractive index of the AQW with the long-wavelength pump beam, changes from 0.225 to 0.316 after considering the conduction-band nonparabolicity. In addition, no redshift is observed. Whether the refractive index of one pump beam with its specific wavelength increases is determined mainly by the linear terms. However, for increasing the other pump wavelengths, the refractive index of one pump beam mainly depends on the nonlinear terms. Subband energy-levels and dipole transition matrix elements show noticeable changes due to conduction-band nonparabolicity, which change the refractive index. Phase matching can be achieved by adjusting the wavelength of the two pump beams. However, both phase mismatch and coverage increase when the conduction band nonparabolicity is considered.

Using nonequilibrium molecular dynamics simulations, we investigate thermal rectification in mass-graded lattices with a new type on-site potential which has a physical picture of the double-well. By adjusting the ratio of harmonic on-site potential and anharmonic on-site potential, we could obtain the optimal heat transport and the best thermal rectification. In addition, we observe the reversal thermal rectification by changing the ratio of on-site potential and analyzes the mechanism of thermal rectification through the power spectrum. At last, we also study the heat flux and thermal rectification in a different case of average temperature and mass gradient.

We investigate the behavior of quantum correlations in some specific Werner-like two-qubit states, where the qubit interacts individually with non-Markovian environment. We employ the local quantum uncertainty and trace distance discord to quantify the amount of quantum correlations between the evolved qubits and the corresponding analytical expressions are derived. For specific values of the parameters characterizing the whole system, the dynamics of quantum correlations exhibits collapse and revival phenomena. The influence of the non-Markovianity is also investigated to analyze the monotonic decay of quantum correlations in the limiting case of Markovian regime. Furthermore, we show that trace distance discord captures quantum correlations that cannot be revealed by local quantum uncertainty in some particular situations.

We study the dynamics of overdamped systems in a symmetric periodic potential against an external load. Using numerical and analytical methods, we show that a symmetric driving signal cannot rectify these systems while an asymmetric one can rectify them, causing its unidirectional rotation. We consider the case where the driving signal is multiharmonic. We find that the mean velocity of the system increases to get the highest value, by appropriate tuning of parameters.