International Journal of Modern Physics B

The heat transfer study in YBa₂Cu₃O${}_{7-\delta }$ superconductors structures is focused on the influence of the effect of scattering events in cross-plane and in-plane references. Understanding the mechanism of controlling the thermal conductivity of layered superconductors is an area of interest for nano microelectronics and thermo-electronic technological applications. The model of the thermal conduction, and phonon transport perpendicular and parallel to the layers of YBa₂Cu₃O${}_{7-\delta }$ are developed. It has been justified via numerical estimation and found substantial diminution in thermal conductivities in both in-plane and cross-plane directions of layered cuprate superconductors.

The structural, electronic, elastic and thermodynamic properties of Curium Monopnictides CmX (X = N, P, As, Sb and Bi) are investigated using first-principles calculations based on the density functional theory (DFT) and full potential linearized augmented plane wave (FP-LAPW) method under ambient condition and high pressure. The exchange-correlation term is treated using two approximations spin-polarized local density approximation (LSDA) and spin-polarized generalized gradient approximation generalized (GGA). The structural parameters such as the equilibrium lattice parameters, bulk modulus and the total energies are calculated in two phases: namely NaCl (B1) and CsCl (B2). The obtained results are compared with the previous theoretical and experimental results. A structural phase transition from B1 phase to B2 phase for Curium pnictides has been obtained. The highest transition pressure is 122 GPa for CmN and the lowest one is 10.0 GPa for CmBi compound. The electronic properties show that these materials exhibit half-metallic behavior in both phases. The magnetic moment is found to be around 7.0 $\mu$B. The mechanical properties of CmX (X = N, P, As, Sb and Bi) are predicted from the calculated elastic constants. Our calculated results are in good agreement with the theoretical results in literature. The effect of pressure and temperature on the thermodynamic properties like the cell volume, bulk modulus and the specific heats C${}_{𝜗}$ and C${}_P$, the entropy ${𝒮}$ and the Grüneisen parameter $\gamma$ have been foreseen at expanded pressure and temperature ranges.

The ferromagnetic (FM) ordering in rutile TiO₂ has been theoretically studied by substituting different $p$-block elements (B, Al, C, Si, N, P and As) doped at oxygen site (B${}_{\mathrm{\text{O}}}$, Al${}_{\mathrm{\text{O}}}$, C${}_{\mathrm{\text{O}}}$, Si${}_{\mathrm{\text{O}}}$, N${}_{\mathrm{\text{O}}}$, P${}_{\mathrm{\text{O}}}$ and As${}_{\mathrm{\text{O}}}$) as well as at titanium site. Ab initio calculations in the frame work of density functional theory indicates that the $p$-block elements (B, C, Al, Si, N, P and As) when substituting the oxygen site give significant amount of magnetic moment, but induce zero magnetic moment in case of substitution at Ti site. Spin–spin interaction for (Ti${}_{12}$O${}_{23}$X)₂ with X = B, Al, C, Si, N, P and As system has also been studied with two different doping distances. Among all the possibilities, carbon substitution at oxygen site (C${}_{\mathrm{\text{O}}}$) results the most stable FM ordering in rutile TiO₂.

In this paper, we introduce the effect of neighbors on the infection of packets by computer virus in the SI and SIR models using the minimal traffic routing protocol. We have applied this model to the Barabasi–Albert network to determine how intrasite and extrasite infection rates affect virus propagation through the traffic flow of information packets in both the free-flow and the congested phases. The numerical results show that when we change the intrasite infection rate ${\lambda }_1$ while keeping constant the extrasite infection rate ${\lambda }_2$, we get normal behavior in the congested phase: in the network, the proportion of infected packets increases to reach a peak and then decreases resulting in a simultaneous increase of the recovered packets. In contrast, when the intrasite infection rate ${\lambda }_1$ is kept fixed, an increase of the extrasite infection rate results in two regimes: The first one is characterized by an increase of the proportion of infected packets until reaching some peak value and then decreases smoothly. The second regime is characterized by an increase of infected packets to some stationary value.

Face-down and face-up bonded polarization-insensitive buried heterojunction superluminescent diode has been studied in terms of thermal behavior and degree of polarization. Our studies have shown that the thermal rollover of current–power characteristic for face-down bonding was about 1.16 times higher than face-up configurations, and face-down bonding can offer higher heat transfer than face-up one. However, face-down bonding will cause more physical stress to the device, and the average value of degree of polarization for face-down bonding devices (35.3%) was much higher than face-up ones (−2.1%). After 48 h high temperature storage at 85${}^{\circ }$C, the stress of face-down devices obtained a better relaxation due to the more stress accumulation.

Current modulation and rectification is an important subject of electronics as well as spintronics. In this paper, an efficient rectifying mesoscopic device is introduced. The device is a two terminal device on the 2D plane of electron gas. The lateral contacts are half-metal ferromagnetic with antiparallel magnetizations and the central channel region is taken as ferromagnetic or normal in the presence of an applied magnetic field. The device functionality is based on the modification of spin-current by tuning the strength of the magnetic field or equivalently by the exchange coupling of the channel to the substrate. The result is that the (spin-) current depends on the polarity of the bias voltage. Converting an alternating bias voltage to direct current is the main achievement of this model device with an additional profit of rectified spin-current. We analyze the results in terms of the spin-dependent barrier in the channel. Detecting the strength of the magnetic field by spin polarization is also suggested.

The stochastic resonance (SR) phenomena of a linear fractional oscillator with random trichotomous mass and random trichotomous frequency are investigate in this paper. By using the Shapiro–Loginov formula and the Laplace transformation technique, the exact expression of the first-order moment of the system’s steady response is derived. The numerical results demonstrate that the evolution of the output amplitude is nonmonotonic with frequency of the periodic signal, noise parameters and fractional order. The generalized SR (GSR) phenomena, including single GSR (SGSR) and doubly GSR (DGSR), and trebly GSR (TGSR), are detected in this fractional system. Then, the GSR regions in the $\alpha -\gamma$ plane are determined through numerical calculations. In addition, the interaction effect of the multiplicative trichotomous noise and memory can diversify the stochastic multiresonance (SMR) phenomena, and induce reverse-resonance phenomena.

A pseudopotential calculation of the electronic structure of Al${}_x$Ga${}_{1-x}$Sb ternary alloys in the zinc-blende structure has been performed. The compositional dependence of energy gaps, electron and heavy hole effective masses and ionicity of the material system of interest have been examined and discussed. Special attention has been given to the effect of the alloy disorder on the direct ($\mathrm{\Gamma }$–$\mathrm{\Gamma }$) bandgap energy. It is found that all features of interest vary monotonically with increasing the Al concentration $x$. Besides, bandgap bowing parameters and extent of the direct-to-indirect bandgap transition have been determined. Our findings agree generally well with the data reported in the literature. Trends in ionicity are found to be consistent with the Phillips ionicity scale.

Employing the tight-binding model, we theoretically study the properties of the plasmon excitations in doped square-lattice atomic clusters. The results show that the dopant atoms would blur the absorption spectra, and give rise to extra plasmon resonant peaks as reported in the literature; however, our calculated external-field induced oscillating charge density shows that no obvious evidences indicate the so-called local mode of plasmon appearing in two-dimensional-doped atomic clusters, but the dopants may change the symmetry of the charge distribution. Furthermore, we show that the disorder of the energy level due to dopant makes the absorption spectrum has a red- or blue-shift, which depends on the position of impurities; disorder of hopping due to dopant makes a blue- or red-shift, a larger (smaller) hopping gives a blue-shift (red-shift); and a larger (smaller) host-dopant and dopant–dopant intersite coulomb repulsion induces a blue-shift (red-shift).

Zn-doped SnO₂ nanoparticles have been synthesized by the chemical precipitation method with the Zn contents ($x$) of 1, 2 and 4 wt.%. The nanoparticles are crystalline in all cases, with the average particle size decreasing from 13.4 nm to 7.71 nm as the Zn concentration increases. The visible photoluminescence emission is observed in Zn-doped SnO₂ nanoparticles, with larger emission intensity at elevated Zn content. The dielectric constant has a strong doping dependence, which is evidently enhanced with increasing Zn content. Magnetization measurements reveal the enhancement in saturation magnetization and remanence magnetization, while the reduction in coercive field is observed with increasing amount of Zn dopant. The variation of optical, dielectric and magnetic properties is due to the incorporation of Zn in SnO₂ with smaller particle size and higher defect density. The present study clearly reveals the doping-induced ferromagnetism in Zn-doped SnO₂ nanoparticles, having applications in ultrahigh dielectric materials, high frequency devices and spintronics.

We investigate the combined effects of trigonal warping and electron–phonon interactions on the renormalization of the Fermi velocity in graphene. We present an analytical solution to the associated Fröhlich Hamiltonian describing the interaction of doubly degenerate-optical phonon modes of graphene with electrons in the presence of trigonal warp within the framework of Lee–Low–Pines theory. On the basis of our model, it is analytically shown that in addition to its renormalization, Fermi velocity exhibits strong anisotropy due to the trigonal warping. It is also found that in the regime where the trigonal warp starts, distortion of energy bands emerges due to electron–phonon coupling, and the bands exhibit strong anisotropy.

This study is motivated by a recent observation, based on photographs from the Cassini mission, that Saturn’s rings have a fractal structure in radial direction. Accordingly, two questions are considered: (1) What Newtonian mechanics argument in support of such a fractal structure of planetary rings is possible? (2) What kinematics model of such fractal rings can be formulated? Both challenges are based on taking planetary rings’ spatial structure as being statistically stationary in time and statistically isotropic in space, but statistically nonstationary in space. An answer to the first challenge is given through an energy analysis of circular rings having a self-generated, noninteger-dimensional mass distribution [V. E. Tarasov, Int. J. Mod Phys. B 19, 4103 (2005)]. The second issue is approached by taking the random field of angular velocity vector of a rotating particle of the ring as a random section of a special vector bundle. Using the theory of group representations, we prove that such a field is completely determined by a sequence of continuous positive-definite matrix-valued functions defined on the Cartesian square $F^2$ of the radial cross-section $F$ of the rings, where $F$ is a fat fractal.