International Journal of Modern Physics B

Structural, electronic, mechanical, thermodynamic and thermoelectric properties of Alkaline fluroperovskites ACdF₃ (A=K, Rb, Cs) have been explored using the FP-LAPW method from the perspective of density functional theory (DFT) as employed in the Wien2k package within the generalized gradient approximation (GGA) as well as the local spin density approximation (LSDA). The volume optimization calculations of these materials agree well with experimental as well as available theoretical values. From the energy dispersion curves as well as DOS plots, all the investigated alkali fluroperovskites are found to have an indirect bandgap in $\mathrm{\Gamma }$-M direction using both approximations. The second-order elastic constants as well as mechanical properties such as Young’s modulus, shear modulus, density, anisotropic factor, B/G${}_{\mathrm{\text{H}}}$ ratio are also computed for these materials. In order to study the thermal and vibrational effects on the studied fluroperovskites, we have employed the quasi-harmonic Debye model that uses a set of energy versus volume calculations. The effects of temperature as well as pressure on the structural parameters are also studied using the non-equilibrium Gibbs function. The transport properties of these perovskites have been investigated using BoltzTrap Code. Comparatively, a good figure of merit of these compounds reveals their possible use in thermoelectric applications.

The structures and magnetic properties of the PP+Fe₃O₄ nanocomposites manufactured by different technological techniques were studied in this work. Polymeric nanocomposite materials based on PP+Fe₃O₄ were obtained by two technological methods: hot pressing and extrusion. Scanning electron microscopy (SEM) and AFM investigations of nanocomposites were carried out for structure analysis. It was found that the distribution of Fe₃O₄ nanoparticles in the polymer matrix for nanocomposites obtained by the hot pressing method is uniform and monodisperse. Compared to this, the heterogeneous and inhomogeneous distribution of nanoparticles in the polymer matrix for the samples that were produced through extrusion method was observed. Furthermore, the nanocomposite samples produced via the extraction method have a lower surface regularity rather than those obtained by hot pressing. M(H) and M(T) studies of polymer nanocomposite samples synthesized through both technological methods were performed. Studies have shown that for relatively low concentrated samples — PP+10% Fe₃O₄, the values of the saturation magnetization were close, but the magnetization of nanocomposites obtained by heat pressing was slightly higher than the other samples. This is because the samples obtained by hot pressing method are characterized by higher uniformity and structure that is called “flat packaging”.

Global warming is an alarming issue in our daily life. As we know that CFCs and HCFCs have a great impact on ozone depletion and global warming process. So, there must be a cheaper way to detect CFCs and HCFCs from refrigerant products like refrigerator, aerosols, air-conditioner, etc. So, for the very first time, this paper proposes a novel highly sensitive dual-core bi-layer gold-coated surface plasmon resonance (DB-SPR)-based photonic crystal fiber (PCF) for sensing CFCs and HCFCs in the field of chemical and biosensing. The analysis is assumed at 20${}^{\circ }$C (293 K) for the concentration level of CFCs and HCFCs ranging between 20% and 80%. The entire numerical evaluation process is done by using finite element method (FEM) with a full vectorial software named COMSOL V-5.1 by examining the number of mesh elements of 228,120 which has better flexibility in the fabrication process. The proposed model can prove itself better than any other models by the justification of the major optical parameters, such as birefringence (B${}_i$), coupling length (L${}_c$), confinement loss (${\alpha }_c$), transmittance (T${}_x$), transmittance variance (T${}_v$), power fraction (P${}_f$), amplitude sensitivity (S${}_A$), wavelength sensitivity (S${}_w$), figure of merit (FOM), resolution (Rl), resonance (R²), etc. which respectively corresponds to their maximum performance profiles of 0.038, 40 $\mu$m, 1140 dB/cm, −180 dB, 410 dB/RIU, 51%, −3200 RIU${}^{-1}$, 30450.43 nm/RIU, 1300, 1.25×10${}^{-5}$, 0.98712. So, it is evident that proposed SPR PCF can be a tough competitor in the field of biosensing and chemical sensing as well as gas sensing.

A new generalized (2+1)-dimensional model, obtained from the Kadomtsev–Petviashvili (KP) equation considered as a system of nonlinear evolution partial differential equations (PDEs), is introduced. With the usage of the Hirota bilinear method and the KP-hierarchy reduction method, N-soliton solutions of the integrable system are constructed. Considering the case of s=−1 in the linear differential operators, L₁ and L₂, and a specific set of parameters, two dark solitons, mixed solutions consisting of soliton-type and periodic waves solution are obtained. Based on the particular definition of the matrix elements, one and two rogue waves solutions expressed in terms of rational functions are derived. It is shown that the fundamental rogue waves are line rogue waves, which is different from the property of the moving line solitons of the soliton equations.

The temperature-dependent structure and dielectric properties of Bi${}_{0.95}$Ba${}_{0.05}$Fe${}_{0.95}$ Ti${}_{0.05}$O₃ ceramic are studied systematically. At the temperature range of 25–800${}^{\circ }$C, the cell parameters are increasing, this indicates its distorted rhombohedral $R$3$c$ structure. A structural phase transformation from rhombohedral $R$3$c$ to cubic Pm3$m$ is observed at 850${}^{\circ }$C. The thermal expansion coefficients in the temperature range 25–700${}^{\circ }$C are calculated. Meanwhile, the temperature-dependent dielectric constant (${𝜀}^{\prime }$) and dielectric loss ($tan\delta$) at different frequencies are measured. This work attempts to show the thermodynamic stability and the effect of charge defects on the electric properties for doped BiFeO₃ ceramics.

Based on the Hirota bilinear form, lump-type solutions, interaction solutions and periodic wave solutions of a (3+1)-dimensional Korteweg–de Vries (KdV) equation are obtained. The interaction between a lump-type soliton and a stripe soliton including two phenomena: fission and fusion, are illustrated. The dynamical behaviors are shown more intuitively by graphics.

In this work, the dielectric and electrical properties of TlInS₂ crystal have been studied in the temperature range of 300–550 K before and after being implanted with H${}^{+}$ ion. The dielectric parameters such as the real and imaginary parts of permittivity, impedance and dielectric loss have been investigated in this temperature range. The role of free ions in the relaxation process when f $<$ 10 kHz on the basis of the study of dielectric parameters in the frequency range of 25–10⁶ Hz has been determined. It has been observed that the interdependencies of the real and imaginary parts of dielectric permittivity go beyond the standard.

The mechanical, electronic and thermodynamic properties of Pd₃M (M=Sc, Y) compounds have been investigated using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. The generalized gradient approximation (GGA) is used to treat the exchange–correlation terms. The calculated formation enthalpies and the cohesive energies reveal that the L1₂ structure is more stable than the D0${}_{24}$ one. The obtained lattice parameters and bulk modulus calculations conform well to the available experimental and theoretical results. The elastic and mechanical properties are analyzed and results show that both compounds are ductile in nature. The Debye temperature and melting temperature are also estimated and are in a good agreement with experimental findings. The total and partial densities of states are determined for L1₂ and D0${}_{24}$ structures. The density of states at the Fermi level, $N$($E_{\mathrm{\text{F}}}$), indicates electronic stability for both compounds. The presence of the pseudo-gap near the Fermi level is suggestive of formation of directional covalent bonding. The number of bonding electrons per atom $n_b$ and the electronic specific heat coefficient $\gamma$ are also determined. The quasi-harmonic Debye model has been used to explore the temperature and pressure effects on the thermodynamic properties for both compounds.

The influences of the dispersion, the impurity and the electron–phonon coupling (EPC) on the properties of the Gaussian confining (GC) potential qubit with magnetic field were studied by Pekar-type variation method. Results show that the decoherence time will increase with increasing the dielectric constant (DC) ratio, the dispersion coefficient and the EPC strength, respectively. The phase rotation quality factor increases with increasing the dielectric constant ratio, the dispersion coefficient and EPC strength, respectively. The magnetic field has a regulatory effect on the decoherence time and the phase rotation quality factor.

The role of relative potential energy of occupied sites in high-order harmonic generation from solid states is investigated. It is found that the conversion efficiency of high-order harmonic spectrum can be enhanced by tuning the relative potential energy of neighboring occupied sites in one-dimensional model. This phenomenon can be attributed to the changing of energy bands. A two-dimensional Kronig–Penney potential is applied to model the salt–rock structure. Similar phenomenon as in the one-dimensional case is also found. Our results provide a potential method to enhance the efficiency of high-order harmonic generation from solids.

Water permeation across a carbon nanotube is important in carbon-based nanodevices. Water transfer rate is closely related to the radius of a carbon nanotube. It is hard to change water transfer rate by interior methods once the radius of the entrance of a carbon nanotube is chosen. In this paper, water transfer across a tandem carbon nanotube with a separation is investigated by molecular dynamics simulations. We find that water transfer rate experiences two different transfer behaviors: an increasing behavior and a decreasing behavior by changing the separation length. The result is important in designing a controllable carbon-based nanodevice.

In this paper, we explore the optical properties of AlGaAs/GaAs semi-parabolic quantum well (QW) under different temperature, hydrostatic pressure and applied magnetic field. We calculate the nonlinear optical absorption coefficients and the refractive index changes (RICs) with the compact density-matrix approach and iterative method. Then, within the framework of the effective mass and parabolic-band approximations, the energy eigenvalues and the corresponding wave functions for semi-parabolic QW have been obtained by the finite difference method. The theoretical findings show that (1) the energy spectrum depends strongly on temperature, hydrostatic pressure and applied magnetic field; (2) the linear and third-order nonlinear optical absorption coefficients and the RICs are quite sensitive to temperature, hydrostatic pressure and applied magnetic field. Our study provides a theoretical basis for the fabrication of QW structure.

The ab initio study of electronic, magnetic properties and Curie temperature of AlAs doped by single and double impurities is investigated using LDA–KKR–CPA method. It is shown that the Al substituted by V and/or Ti induces a half-metallic character and ferromagnetism in the system for different concentrations except co-doping by x=y=0.035. The stability of magnetism between the ferromagnetic and DLM states as well as the mechanism of exchange interaction are discussed. The density of states are plotted in the energy diagram for different concentrations of dopants. The co-doping with (V, Ti) increases Curie temperature in AlAs with respect to single substituant. The finding of this work confirms that the new compounds have a great potential for spintronic devices.

For stochastic quantum systems with given dissipations, the identification method of Hamiltonian is given in this paper. First, the stability of the system is realized through designing a real-time feedback control method. Second, by using Routh–Hurwitz stability criterion, the intervals of the element values of the system Hamiltonians are given. Finally, the identification of Hamiltonian is realized by selecting the equilibrium state of the system equal to the desired target state. For two typical categories of noise: Purely dephasing decoherence and amplitude damping decoherence, we check the validity of the proposed estimation scheme.