International Journal of Modern Physics B

The phase behavior of the melt of the symmetric V-shaped molecules has been inspected within the Landau–de Gennes approach. The arms of V-shaped molecule are modeled by rod-like segments connected at an external angle $\alpha$; these segments are assumed to be composed of monomer units. The phase diagram of the system contains regions of stability of the isotropic, homogeneous nematic, and modulated nematic phases: nematic twist bend (N${}_{\mathrm{\text{TB}}}$) phase that is characterized by the three directors which move on a helix and one of these directors forms a fixed nonzero cone angle with the helix axis, and the N₀ modulated phase in which one director is parallel to the helix axis while two others are orthogonal to the helix axis. The characteristic periods of modulated structures were found to be of order a few molecular lengths.

We consider the stationary state properties of pseudo-spin-1/2 rotating dipolar Bose–Einstein condensates (BECs) by numerical simulations of the Gross–Pitaevskii equation. Different vortex structures in each component are studied, depending on the competition between the dipole–dipole interactions (DDIs) and rotational. We also investigate the differences of vortex number in the two components, showing that anisotropic nature of DDIs plays a significant role in vortices formation process.

In this paper, low temperature, economical sol–gel combustion method was adopted to synthesize wollastonite ceramic. Calcium nitrate tetrahydrate and tetraethyl orthosilicate were taken as source for Ca and Si, while citric acid and nitric acid were used as chelating/combustion agents. The yielded powder calcined at 600${}^{\circ }$C for 4 h was characterized by FTIR, XRD and SEM techniques. Results showed that the citrate combustion method was the most efficient method to prepare wollastonite at low temperature. Moreover, in vitro bioactivity test performed in simulated body fluid (SBF) showed good bioactivity of synthesized wollastonite ceramics.

The aim of this study is to discuss the effect of moisture absorption on electrical conductivity and electromagnetic interference of the carbon fiber (CF) reinforced bioplastic composite. The composites were prepared by the hot press machine, and immersed in water for 20 and 40 days. The electrical conductivity measurements were carried out as a function immersed time. The electrical conductivity of CF with two layers is greater than that of one layer, because the electrical conductivity increases with increasing the volume filler of CF. The electrical conductivity slightly increases with increasing the immersion time. The EMI SE (electromagnetic interference shielding effectiveness) of the composite was examined with the frequency from 500 MHz to 2000 MHz. The EMI SE of the CF increases with increasing the content of the CF, and the EMI SE result of composite is around 50 dB to 60 dB. There is scarcely significant effect of orientation on composite on the EMI SE.

In the presented work, nanocomposites based on poly (vinylidene fluoride) (PVDF) and magnetite Fe₃O₄ nanoparticles were prepared. The structure and content of nanocomposite materials were studied by using scanning electron microscope (SEM), atomic-force microscope (AFM) and X-Ray diffraction (XRD). Magnetic properties of PVDF+Fe₃O₄ nanocomposites have been studied upon increasing nanoparticle content in polymer matrix upto 20%, revealing superparamagnetic behavior as Fe₃O₄ nanoparticles in polymer matrix act out like single-domain particles. It has also been observed that PVDF+Fe₃O₄-based nanocomposites can absorb the electromagnetic waves in the high frequency range 0.1–30 GHz. It has been shown that the absorption of high frequency radio waves by PVDF+Fe₃O₄ nanocomposites can be explained by the different molecular structures and also by the scattering of the radio waves at the boundary of nanoparticle-polymer matrix.

We report the results of first-principles calculations regarding the structural parameters, elastic moduli, electronic structure and optical properties of the ternary rhombohedral layered compounds, KLaSe₂ and RbLaSe₂. These calculations were performed by employing the pseudo-potential plane-wave (PP-PW) method. Although the calculated structural parameters (a, c, V, c/a, bond-length d) using different exchange and correlation approximations are found in nice harmony with the available experimental data, the best agreement is obtained with the GGA-PW91 functional. The effect of the K–Rb substitution is noted very clearly on the degree of ionic bonding of the A–Se bond (A=K, Rb). The electronic band structure and the density of states (DoS) plots reveal the semiconducting characteristics of both compounds with an indirect bandgap energy, E${}_g$ of about 2 eV. The mechanical stability of the ALaSe₂ compounds is investigated for the first time by calculating the single-crystal elastic constants C${}_{ij}$ using the stress-strain approach. In order to understand the linear optical properties of the studied systems, frequency-dependent polarized optical functions were computed for an energy range from 0.0 eV to 18 eV. Our calculated optical spectra reveal the isotropic nature of the optical properties of the ALaSe₂ compounds.

In this paper, both the fifth-order Runge–Kutta numerical scheme and binary collision approximation are used to study the phase shift. Both numerical and theoretical results are shown that the solitary wave after head-on collision propagates along the chain behind the reference wave in both even and odd numbers of grain chains. It is the well-known feature of the appearance of the phase shift. Those results are in agreement with the experimental results. Furthermore, it is found that the phase shift is not only related to the collision position of the waves, but also to the position where the time is measured. The value of phase shift increases nonmonotonously with increasing the velocity of the opposite propagation of the wave. Binary collision approximation is applied to analyze the phase shift, and it is found that theoretical results agree well with numerical results, especially in the case of phase shift in odd chain.

This paper investigates the clustering problem for the generalized signed networks. By rigorous derivations, a sufficient and necessary condition for clustering of the nodes in generalized signed networks is proposed in this paper. In order to obtain this condition, the concept of friends group is first introduced for the nodes based on their links’ sign. Then, the unprivileged network is also defined in this paper by employing the concepts of structural hole and broker. Compared with the existing clustering algorithms, the outstanding advantage in this paper is that only the positive or negative (especially, or zero) sign of the links is required regardless of their density or sparsity. We have proved mathematically that a generalized signed network is classifiable if and only if it is an unprivileged network. Finally, two examples associated with numerical simulations are proposed to generate the unprivileged networks.

We study the ground state of spin-2 dipolar rotating Bose–Einstein condensates in a harmonic potential. As the strength of dipolar interaction enhances, our results show that the vortex number becomes smaller and smaller at a fixed component. In addition, the vortex stripe occurs and its number increases. The components m${}_F=\pm$1 or ±2 display the same density and the total density shows layered distribution. Increasing the rotational frequency to a higher value, the vortex number and vortex row number increase. We also plot the dependence of angular momentum L_z as a function of dipole strength c${}_d^{\prime }$, showing that L_z decreases with increasing c${}_d^{\prime }$.

Thermophysical properties of phase change material NaCl and KCl were calculated using molecular dynamics (MD) simulations and a recent EIM interatomic potential. Density, thermal expansion coefficient, specific heat capacity were computed using equilibrium MD (EMD) simulations. The results are very close to the experimental values. The thermal conductivity was computed using two non-equilibrium MD (NEMD) methods and the results were compared with the experimental data. They appear to be relatively reasonable. Binary NaCl/KCl systems have also been investigated. The specific heat capacity with different compositions are calculated. They are very close with recent experimental results.

The emergence of online social networks has revolutionized millions of web users’ behavior so that their interactions with each other produce huge amounts of data on different activities. Community detection, herein, is one of the most important tasks. The very recent trend is to detect meaningful communities based on users’ interactions or the activity network. However, in many of such studies, authors consider the basic network model while almost ignoring the model of the interactions in the multi-layer network. In this research, an experimental study is done to compare community detection in Facebook friendship network to that of activity network, considering different activities in Facebook OSN such as sharing. Then, a new community detection evaluation metric based on homophily is proposed. Eventually, a new method of community detection based on different activities in Facebook social network is presented. In this method, we generalized three familiar similarity methods, Jaccard, Common Neighbors and Adamic-Adar for multi-layered network model.

To observe the effect of halogen-substitution on the Mn-O electron transfer of NiMn₂O₄, we calculated Mn-mixed-valence configuration (charge-disproportionation) and oxygen vacancy by the density functional theory (DFT). The results indicate that the halogen-p⁵ state induces the O-2p orbital splitting to create an oxygen vacancy in the VB (valence band: about −5 eV). The oxygen vacancy can capture an electron from Mn${}^{3+}$-3d⁵ orbital that makes the Mn${}^{3+}$-3d⁵ change to Mn${}^{4+}$-3d⁴ states (Mn-charge disproportionate), and providing many effective-hole (40.14 $\sim$ 96.72 × 10${}^{-31}$ kg). The halogen-p⁵-O-2p⁴ hybrid orbitals enhance the O-2p⁴-Mn-3d⁵ p-d hybrid orbital (about 19.18 electron). That increases the surface potential in Mn-O octahedron (for Cl-substituted: about 60 meV), the corresponding electron–electron interactions change from complex t${}_{2g}$ (O-2p⁴-Mn${}^{3+}$-3d${}^5)$ to complete $t_{2g}$ (O-2p⁴-Mn${}^{4+}$-3d${}^4)$-e${}_g$(O-2p⁴-halogen-p⁵) orbital. This study effectively analyzes the microscopic changes of the electron transfer caused by the small amount of doping, provides a theoretical basis for the design of NMO-based semiconductor material.

An Eshelby particle-compounded model was employed to investigate the stress distribution in the SiCp/Fe composites during straining in order to predict the stress-strain curves of the composites. Effect of the SiC volume content and aspect ratios on yield strength of the SiCp/Fe composites was studied by the simulation. The modeling results indicate that the stress in the iron matrix is much smaller than that in SiC particles as straining the composites, which means the strengthening mechanisms of the SiCp/Fe composites is determined by the load transfer mechanisms. The aspect ratios of the particles play a significant role in yield strength of the SiCp/Fe composites especially as the particle volume content is large. The stress in SiC particles has a stronger dependence on the aspect ratios of the particles only if the reinforcement volume content is small.

An electric interfacial layer appears when the mobile ions or nanoparticles of an electrolyte solution interact with an extended, charged surface. The distribution of ions or nanoparticles is driven by electrostatic interactions and entropy. We consider continuously charged spherical nanoparticles of finite size. At thermodynamic equilibrium, the spatial profile of the concentration is obtained by deriving the appropriate Euler–Lagrange equations. We discuss how various model parameters of the nanoparticles influence structural properties of the electric interfacial layer. We calculate the pressure between two like-charged surfaces embedded in a water solution of continuously charged spherical nanoparticles.