International Journal of Modern Physics B

Two-dimensional disclinated atomic graphene layer in curved space–time is exactly discussed, and the explicit dependence of Landau levels on the topological defect and external magnetic field are obtained in the presence of nonuniform magnetic field. It is worth mentioning that the presence of topological defect reduces the degeneracy of energy levels. The persistent current, magnetization, susceptibility and the magnetoresistance of structure are investigated. It can be shown that the curvature of the conical surface affects the pattern of oscillations of persistent current and, of course, corresponding magnetoresistance. The behavior of the above physical quantities as a function of magnetic flux is explicitly found for various defects. We observe that increasing magnetic field leads to a aperiodic oscillation. The large Aharonov–Bohm flux gives rise to vanish the magnetization oscillations.

Iron (Fe)-based nanoparticles are extremely valuable in biomedical applications owing to their low toxicity and high magnetization values at room temperature. In this study, we synthesized nearly monodisperse iron oxide (Fe₃O₄) and Fe@Fe₃O₄ (core: Fe, shell: Fe₃O${}_4)$ nanoparticles in aqueous medium under argon flow and then, coated them with various biocompatible ligands and silica. In this study, eight types of surface-modified nanoparticles were investigated, namely, Fe₃O₄@PAA (PAA = polyacrylic acid; $M_w$ of PAA = 5100 amu and 15,000 amu), Fe₃O₄@PAA–FA (FA = folic acid; $M_w$ of PAA = 5100 amu and 15,000 amu), Fe₃O₄@PEI–fluorescein (PEI = polyethylenimine; $M_w$ of PEI = 1300 amu), Fe@Fe₃O₄@PEI ($M_w$ of PEI = 10,000 amu), Fe₃O₄@SiO₂ and Fe@Fe₃O₄@SiO₂ nanoparticles. We characterized the prepared surface-modified nanoparticles using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) absorption spectroscopy, a superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and confocal microscopy. Finally, we measured the cytotoxicity of the samples. The results indicate that the surface-modified nanoparticles are biocompatible and are potential candidates for various biomedical applications.

A group of ABO₃ perovskite-type oxides is currently under intensive studies for their potential as chemical sensing, ferroelectric memories, gas separation and computer devices. This group includes La${}_x$Sr${}_{1-x}$CoO₃ (LSCO). In the present work, we have synthesized LSCO samples by using the sol–gel method and studied their nano structural and electrical properties with using the scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Current density–voltage ($J$–$V$) and Fourier transform infrared spectroscopy (FTIR) techniques. We synthesized nanoparticles with diameters between 50 and 100 nm by calcination of the pulverized gel powders, and then studied its structure. The band gap characteristics of the La${}_{0.5}$Sr${}_{0.5}$CoO₃ structure were also analyzed. The obtained results show that La${}_{0.5}$Sr${}_{0.5}$CoO₃ with favorable carrier mobility ($\sim 1.7\times 10^{-2}$ cm²v${}^{-2}$s${}^{-1}$) and dielectric constant (16) exhibits a variety of interesting physical properties which include ferroelectric, dielectric, pyroelectric and piezoelectric behavior.

Due to its geometry simplicity, the forces of thin liquid film are widely investigated and equivalently employed to explore the phys–chemical properties and mechanical stability of many other surfaces or colloid ensembles. The surface tension of bulk liquid (${\sigma }_{\infty }$) and film tension ($\gamma$) are the most important parameters. Considering the insufficiency of detailed interpretation of film tension under micro-scale circumstances, a method for film tension was proposed based on numerical modeling. Assuming surface tension at different slab thicknesses being identical to the surface tension of film, the surface tension and disjoining pressure were subsequently used to evaluate the film tension based on the derivation of film thermodynamics, and a decreasing tendency was discovered for low temperature regions. The influence of saline concentration on nano-films was also investigated, and the comparison of film tensions suggested that higher concentration yielded larger film tension, with stronger decreasing intensity as a function of film thickness. Meanwhile, at thick film range (15–20 nm), film tension of higher concentration film continued to decrease as thickness increase, however it arrived to constant value for that of lower concentration. Finally, it was found that the film tension was almost independent on the film curvature, but varied with the thickness. The approach is applicable to symmetric emulsion films containing surfactants and bi-layer lipid films.

Electron properties of semiconducting zigzag carbon nanotubes (CNTs) can be described by two uncoupled Dirac equations of dimension (1+1) for the particle with nonzero mass. The solutions of these equations are two charge-neutral Majorana fields. An analogous equation is obtained for the carbon chains. We use the approach, wherein wavefunction of charged particle is represented as the production of a rapidly oscillating exponent and the slowly varying function amplitude depending on the longitudinal coordinate.

This paper concerns the vibrational behavior of concentric double-walled and triple-walled carbon and boron nitride nanotubes using the finite element method. Armchair and zigzag nanotubes with different lengths and diameters are considered. Moreover, different boundary conditions are applied on the nanotubes. It is observed that in double-walled nanotubes, when the inner and outer layers are respectively from boron nitride and carbon, the frequencies are larger than those in the reverse arrangement. Investigating the effect of diameter on the first 10 natural frequencies of double-walled and triple-walled nanotubes showed that nanotubes with larger diameters possess smaller frequencies. The effect of diameter is more significant for higher modes. Finally, comparisons are made between the vibrational behavior of concentric carbon and boron nitride double-walled and triple-walled nanotubes. Considering the effect of vacancy defect on the vibrational characteristics of the nanotubes revealed that when all of the walls of the nanotubes are defective, the largest diminish occurs for the fundamental natural frequencies.

Positron annihilation technique is applied to study the recovery of radiation-induced defects in 140 MeV oxygen (O${}^{6+}$) irradiated Fe-doped semi-insulating indium phosphide during annealing over a temperature region of 25${}^{\circ }$C–650${}^{\circ }$C. Lifetime spectra of the irradiated sample are fitted with three lifetime components. Trapping model analysis is used to characterize defect states corresponding to the de-convoluted lifetime values. After irradiation, the observed average lifetime of positron ${\tau }_{\mathrm{\text{avg}}}=263$ ps at room temperature is higher than the bulk lifetime by 21 ps which reveals the presence of radiation-induced defects in the material. A decrease in ${\tau }_{\mathrm{\text{avg}}}$ occurs during room temperature 25${}^{\circ }$C to 200${}^{\circ }$C indicating the dissociation of higher order defects, might be due to positron trapping in acceptor-type of defects ($V_{\mathrm{\text{In}}}$). A reverse annealing stage is found at temperature range of 250${}^{\circ }$C–425${}^{\circ }$C for $S$-parameter probably due to the migration of vacancies and the formation of vacancy clusters. Increase in $R$-parameter from 325${}^{\circ }$C to 425${}^{\circ }$C indicates the change in the nature of predominant positron trapping sites. Beyond 425${}^{\circ }$C, ${\tau }_{\mathrm{\text{avg}}}$, $S$-parameter and $R$-parameter starts decreasing and around 650${}^{\circ }$C, ${\tau }_{\mathrm{\text{avg}}}$ and $S$-parameter approached almost the bulk value showing the annealing out of radiation-induced defects.

In present paper, it is focused on theoretical study of TiO₂ with particular emphasis on vibrational phonon properties by means of van der Waals three-body force shell model (VTBFSM). Present model includes van der Waals interactions (VWI) and three-body interactions (TBI) in the framework of both ion polarizable rigid shell model (RSM) with short-range interactions effective up to the second neighbor. The Coulombic ion–ion interaction contribution to the dynamical matrix is calculated by the Kellerman.¹ Therefore, it may be inferred that the present model is the most realistic model for complete harmonic dynamical behavior of the crystals. The lattice dynamical study of phonon properties of transition metal titanium dioxide (TiO₂) has been presented by means of VTBFS model. Titanium is an extremely light semiconducting material, exhibiting stable bcc structure in a certain temperature range 0–300 K normal pressures Debye temperature variation and combined density of states (CDS) of TiO₂ has been studied in this work. At high temperature, strength and oxidation resistance of Ti alloys has improved. The model predictions are found to be in reasonable agreement with experimental data.²

Weighted and unweighted networks composed of coupled bistable oscillators with small-world topology are investigated under the co-presence of a weak signal and multiplicative Gaussian white noise. As the noise intensity is adjusted to one or two optimal values, the temporal periodicity of the output of the system reaches the maximum, indicating the occurrence of stochastic resonance (SR) or stochastic bi-resonance (SBR). The resonance behavior is strongly-dependent on the coupling strength in both networks. At a weak coupling, SR more likely takes place; whereas at a strong coupling, SBR is prone to occur. Compared with unweighted networks, the span of coupling strength for SBR is narrower in weighted networks. In addition, the weak signal cannot be amplified so effectively in the weighted networks as in the unweighted networks, attributing to the weakening effect of the link weight on the coupling between oscillators and the heterogeneity of the whole network connectivity caused by the weight distribution.