Modern Physics Letters B

Employing a first-principles method in combination with the empirical criterions, we have investigated the site preference of boron (B) and its effect on the mechanical properties of the binary-phase TiAl–Ti₃Al alloy. It is found that B energetically prefers to occupy the Ti-rich octahedral interstitial site, because B is more favorable to bond with Ti in comparison with Al. The occupancy tendency of B in the TiAl–Ti₃Al alloy is the TiAl/Ti₃Al interface $>$ Ti₃Al $>$ TiAl, thus B tends to segregate into the binary-phase interface in the TiAl–Ti₃Al alloy. The charge density difference shows that B at the TiAl–Ti₃Al interface will form strong B–Ti bonds and weak B–Al bonds, leading to the significant increasing of the cleavage energy $({\gamma }_{\mathrm{\text{cl}}})$ and the unstable stacking fault energy $({\gamma }_{\mathrm{\text{us}}})$. This indicates that the presence of B will strengthen the TiAl/Ti₃Al interface, but block its mobility. Further, the ratio of ${\gamma }_{\mathrm{\text{cl}}}$/${\gamma }_{\mathrm{\text{us}}}$ of the B-doped system is 4.63%, 8.19% lower than that of the clean system. Based on the empirical criterions, B will have a negative effect on the ductility of the TiAl–Ti₃Al alloy.

The isotope shifts of the $2s{}^2{\mathrm{\text{S}}}_{1/2}$–$2p{}^2{\mathrm{\text{P}}}_J(J=1/2,3/2)$ transitions for the Li-like neutron-rich and neutron-deficient ${}^{21\text{–}32}\mathrm{\text{Mg}}$ isotopes are calculated using the multi-configuration Dirac–Hartree–Fock (MCDHF) method and the relativistic configuration interaction approach. The results provided herein can be employed for the consistency check with the nuclear root-mean-square (rms) nuclear charge radii of the short-lived magnesium isotopes from the experimental isotope shifts using the corresponding transitions. The methods used here could also be applied to other few-electron Li-like systems and the analogous isotope shift results could be obtained.

Co/NM (nonmagnetic Ag and SiO₂)/Co sandwich structure films with different thicknesses of NM were fabricated on Si(111) substrate via oblique radio frequency sputtering. With increasing thickness of nonmagnetic Ag $(t_{\mathrm{\text{Ag}}})$, in-plane magnetic anisotropy field $H_k$ initially increased from 100 Oe of $t_{\mathrm{\text{Ag}}}=0$ nm to 220 Oe of $t_{\mathrm{\text{Ag}}}=1.5$ nm, and then decreased when $t_{\mathrm{\text{Ag}}}>1.5$ nm. Resonance frequency showed the same tendency with maximum 5.2 GHz when $t_{\mathrm{\text{Ag}}}=1.5$ nm. Damp factor increased from 0.02 for $t_{\mathrm{\text{Ag}}}=0\text{–}0.08$ for $t_{\mathrm{\text{Ag}}}=2.0$ nm. The same result was observed in inserting oxide nonmagnetic SiO₂ layer. This can be attributed to the competition between interface energy and exchange coupling energy.

Propagation of few-cycle optical Airy pulse through the array of semiconductor carbon nanotubes (CNTs) is considered. CNTs are supposed to contain multilevel impurities. In our study, we have neglected transitions between the valence and the conduction bands. As a result, we have revealed the dependence of the pulse form on the parameters of energy.

Manganese oxides are of more interest to researchers because of their ability as catalysts and lithium batteries. In this research, MnO₂ nanowires with diameter about 45 nm were synthesized by sol–gel method at room temperature (RT). Effect of increasing the annealing temperature from 400${}^{\circ }$C to 600${}^{\circ }$C on crystalline structure of nanostructure were studied and average crystallite size was estimated about 22 nm. X-ray Diffraction (XRD) method, Energy-Dispersive X-ray Diffraction (EDXD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM) were used to characterize the nanowires of MnO₂.

Quantum entanglement is discussed as a consequence of the quantization of fields. The inclusion of quantum fields self-consistently explains some quantum paradoxes (EPR and Hardy’s paradox). The definition of entanglement was introduced, which depends on the maximum energy of the interaction of particles. The destruction of entanglement is caused by the creation and annihilation of particles. On this basis, an algorithm for quantum particle evolution was formulated.

In the paper, the fixed-time and finite-time synchronizations of multi-links complex network are investigated. Compared with finite-time synchronization, the settling time of fixed-time synchronization is independent of initial conditions. For uncertain multi-links complex networks, this paper further analyzes synchronization mechanism and unknown parameters based on the drive-response concept and finite-time stability theory. Novel synchronization control criteria and the result of parameters identification are, respectively, obtained in a finite time by utilizing Lyapunov function and linear matrix inequality (LMI). Besides, we give other two versions of finite-time synchronization and parameters identification for uncertain multi-links complex network with impulsive control input. Finally, numerical examples are given to illustrate the effectiveness of our theoretical results.

A combination of density functional theory and non-equilibrium Green’s function methods are used to simulate spin-dependent electronic transport in monatomic Au-nanowires sandwiched between ferromagnetic electrodes. Electrodes of the junction are in turn composed of tetragonal FeCo, FePd and FePt alloys. Magnetic anisotropy energies of the electrodes are calculated for different values of the c/a ratios of the electrode lattice constants and it is shown that at c/a = 1.05, the FePt electrodes gain a relatively large amount of magnetic anisotropy energy (MAE). Hence, it is concluded that the ferromagnetic FePt alloy can be used as a suitable type of electrode for applications in perpendicular magnetic tunnel junctions (MTJs). We observe that increasing the c/a ratio leads to notable improvements in the spin filtering of the FeCo and FePd MTJs while it only has a slight effect on the filtering of the FePt MTJ. Later, we show that by removing the interfacial Pt atoms of the FePt MTJ, we are able to enhance its filtering property.

A model is proposed to study the size and shape effects on specific heat and thermal conductivity of nanomaterials. The formulation developed for specific heat is based on the basic concept of cohesive energy and melting temperature. The specific heat of Ag and Au nanoparticles is reported and the effect of size and shape has been studied. We observed that specific heat increases with the reduction of particle size having maximum shape effect for spherical nanoparticle. To provide a more critical test, we extended our model to study the thermal conductivity and used it for the study of Si, diamond, Cu, Ni, Ar, ZrO₂, BaTiO₃ and SrTiO₃ nanomaterials. A significant reduction is found in the thermal conductivity for nanomaterials by decreasing the size. The model predictions are consistent with the available experimental and simulation results. This demonstrates the suitability of the model proposed in this paper.

The Vogel–Fulcher–Tamman (VFT) correlation is the known most accurate equation used to estimate and predict temperature-dependent viscosity of fluids. But its accuracy analysis for saturated liquids is still unknown. In this paper, we checked its ability for 49 saturated liquids by using the data in the National Institute of Standards and Technology (NIST) Webbook. Through detailed accuracy analysis, we found that the VFT correlation works qualitatively but does not work well quantitavely. We shown the temperature ranges in which the VFT correlation holds for absolute average deviations (AADs) of $\sim$1%, $\sim$2% and $\sim$5%. The corresponding coefficients are also obtained for engineers to use it directly. We also proposed a new four-parameter correlation to improve the predictive ability. We show that the new correlation holds for 5 fluids with AAD $<$ 1%, 37 fluids with AAD $<$ 2%, 43 fluids with AAD $<$ 3% and 48 fluids with AAD $<$ 4%.