Modern Physics Letters B

This paper outlines general physical issues associated with performing computational numerical simulations of primary point defects in MAX phases Ti₂AlN. First-principles solutions are possible due to the development of computational resources of software and hardware. The calculation accuracy is a good agreement with the experimental results. As an important application of our simulations, the results could provide a theoretical guidance for future experiments and application of Ti₂AlN. For example, the N mono-vacancy is the most difficult to form. On the contrary, the mono-vacancy formation in Ti₂AlN is energetically most favorable for the Al atom. The essence of the phenomena is explained by the calculated density of state (DOS).

In this paper, we investigate the effect of vacancy defects on spin transport in graphene-based magnetic tunnel junction (MTJ). An increase in conductance was seen in vacancy-defected MTJ structure which is in contrast to the results reported in past where a decrease in conductance with vacancy was observed for graphene sheets. This increase in conductance may be due to the use of CrO₂ half-metallic ferromagnet (HMF) electrodes instead of metallic or ferromagnet (FM) electrodes. Furthermore, high tunnel magnetoresistance (TMR) $\sim$99% and perfect spin filtration was obtained for both vacancy-defected and no-defect (pristine) MTJ structures. The TMR in vacancy-defected structure is seen to decrease by 6.2% and by 13% at bias voltages of 1.2V and 1.4V, when compared to TMR in no-defect MTJ structure.

Under investigation in this paper is a variable-coefficient Gross–Pitaevskii equation which describes the Bose–Einstein condensate. Lax pair, bilinear forms and bilinear Bäcklund transformation for the equation under some integrable conditions are derived. Based on the Lax pair and bilinear forms, double Wronskian solutions are constructed and verified. The $N$th-order nonautonomous solitons in terms of the double Wronskian determinant are given. Propagation and interaction for the first- and second-order nonautonomous solitons are discussed from three cases. Amplitudes of the first- and second-order nonautonomous solitons are affected by a real parameter related to the variable coefficients, but independent of the gain-or-loss coefficient $m_0(t)$ and linear external potential coefficient $m_1(t)$. For Case 1 $[m_0(t)=0]$, $m_1(t)$ leads to the accelerated propagation of nonautonomous solitons. Parabolic-, cubic-, exponential- and cosine-type nonautonomous solitons are exhibited due to the different choices of $m_1(t)$. For Case 2 $[m_1(t)=0]$, if the real part of the spectral parameter equals 0, stationary soliton can be formed. If we take the harmonic external potential coefficient $m_2(t)$ as a positive constant and let the real parts of the two spectral parameters be the same, bound-state-like structures can be formed, but there are only one attractive and two repulsive procedures. For Case 3 [$m_0(t)$ and $m_1(t)$ are taken as nonzero constants], head-on interaction, overtaking interaction and bound-state structure can be formed based on the signs of the two spectral parameters.

By applying the Chen–Möbius inversion method, a concise formula is introduced to get the pair potentials of the Ag/Si(111) interface by inversion of the ab initio adhesive energies. The check shows that the inversed potentials are self-consistent. Then, by using the interfacial potentials obtained, we analyze the changes of the energy, stress and atomic structures, giving a detailed presentation of the fracture process about the Ag/Si(111) interface. Meanwhile, we know that there are three kinds of fracture mode. In this work, the fracture process is performed in mode II (shear).

In this paper, we analytically find the ground states of a mixture of two species of pseudospin-$\frac{1}{2}$ Bose gases with interspecies spin exchange in quite generic parameter regimes. In the most interesting phase, the ground state is strongly entangled between the two species in a very wide parameter regime, and is an entangled Bose-Einstein condensate. The phase diagram and elementary excitations are studied.

The site preference of X (X = Mn, Fe, Co, Cu) in NiAl and its effects on structural, electronic and elastic properties were investigated by performing first-principles calculations using density functional theory (DFT). Formation enthalpy calculations show that adding X increases the formation enthalpy of NiAl, indicating that X addition reduces the stability of system. The site preference was investigated by calculating the transfer energy of NiAl alloys with X. The results further exhibit that Mn, Fe and Cu show no site preference, but Co tends to occupy Ni site. By analyzing electronic density of states, Mulliken population, overlap population and valence charge density, the electronic property and bond characters were discussed. The elastic property calculation shows that only substitution of Ni by Cu increased the plasticity of alloy, while in the other cases the plasticity was decreased.

Flocking behavior of animals is highly advantageous for taking food resources. The degree of the advantage is related to the ability of flock members to detect their prey and the mobility of prey individuals. In this study, to explore the relation, we constructed a model to simulate a predator flock and its randomly moving prey. The predator members have the prey detection ability, which was characterized as sensing distance, $R$, and a sensing angle, $\theta$. The mobility of the prey individuals was characterized as the maximum traveling distance of an iteration time step, $L$. The relative flock foraging efficiency, $\epsilon$, was defined as $\epsilon =1-(T_d/T_{\mathrm{\text{up}}})$. $T_{\mathrm{\text{up}}}$ and $T_d$ represent the spent time for the flock to eat all prey individuals and to uptake the last remaining 10% prey, respectively. Simulation results showed that $\epsilon$ increased, maximized, and decreased with the increase of $R$, regardless of $L$. As the number of prey, $N$, increased, the tendency of the increasing and decreasing was diluted. The result was briefly discussed in relation to the flock foraging behavior and the development of the model toward applications for real ecosystems.

Bi₄Ti₃O${}_{12}$ (BIT) and Bi${}_{3.25}$Nd${}_{0.75}$Ti₃O${}_{12}$ (BNT) thin films were deposited on Pt/Ti/SiO₂/Si (100) substrates using pulsed laser deposition. The surface morphologies, ferroelectric domain structures and polarization switching were investigated by atomic force microscopy (AFM) and piezoelectric force microscopy (PFM). The phase and amplitude images of PFM show that the BIT and BNT thin films have clear domain structures. Comparison of the surface morphologies and domain structures indicates that the grain boundaries limit the shape of domain and affect the domain structure. The micro-electromechanical performance was characterized by the effective piezoelectric coefficient $d_{33,f}$ of the thin films. The result shows that the maximum effective $d_{33,f}$ value (100 pm/V) of BNT thin film is larger than that of BIT thin film (30 pm/V). This can be ascribed to BNT thin film with a preferred growth direction of $a$-axis, resulting in effective enhancement of $d_{33,f}$. Besides, all the thin films exhibit good optical transmittance in the range of 500–800 nm and the optical band gaps increase from 3.43 eV to 3.52 eV due to Nd doping.

In this paper, an ultrasound assisted solid state synthesis method for high-temperature (HT${}_c$) YBa₂Cu₃O${}_{7-x}$ (YBCO) superconductor nanostructures with different morphologies is presented. Here, the routine heat treatment of the powder mixture of as-prepared precursors is followed by the ultrasound irradiation inside various alcoholic solutions. Not only the influence of the ultrasound irradiation intensity and duration but also the influence of different solvents such as ethanol, methanol and 1-butanol with various vapor pressures and so various destruction powers were also studied on the morphology and particle size of the products. The various morphologies were studied by scanning electron microscope (SEM) which not only have been affected by intensity and type of alcoholic solvent but also sonication time and ultrasound power have significant role as well. Formation of the YBCO superconducting phase was examined by using Rietveld refinement of X-ray diffraction (XRD) which indicates the crystalline preferred growth in $c$-axis orientation in crystal. Magnetic susceptibility measurements showed the ultrasound waves had no important effect on the onset critical temperature of the prepared nanorods (about 91.64 K) which is compared with the bulk samples $(T_c\sim 92\mathrm{\text{K}})$.

Coherent pulse is used to control and measure the quantum state of three-level system in double quantum dots. We analyze the coherent oscillations in Landau–Zener–Stueckelberg (LZS) dynamics by the adiabatic-impulse model, which simplifies the applied pulse as an optical interference device. Under the designed “hat-shape” pulse, the sweeping speed through each avoid crossing can be tuned independently. The coherent oscillations in LZS dynamics of three-level system are optimized by the control pulse. Moreover, we can filter out the coherent oscillations with the unexpected frequency and only keep the coherent oscillations with the frequency we are interested in.

In this paper, S-doped vanadium oxide thin films with doping levels up to 40 at.% are prepared via spray pyrolysis method on glass substrates, and the effect of S-doping on the structural and photoconductivity related properties of $\beta$-V₂O₅ thin films is studied. The results show that most of the films have been grown in the tetragonal $\beta$-V₂O₅ phase structure with the preferred orientation along [200]. With increasing the doping level, the samples tend to be amorphous. The structure of the samples reveals to be nanobelt-shaped whose width decreases from nearly 100 nm to 40 nm with S concentration. The photoconductivity measurements show that by increasing the S-doping level, the photosensitivity increases, which is due to the prolonged electron’s lifetime as a result of enhanced defect states acting as trap levels.

In this paper, we have proposed a novel periodic surface plasmon polariton (SPP) waveguide to realize a one-way mode converter which is based on a parity–time (PT) symmetry broken system, and it converts the fundamental TM mode to the first-order TM mode in only forward direction. Periodic gain potentials are put in place to construct the system mentioned in periodic SPP waveguide. Further, as the mode converter contains gain and loss material, light signals will be amplified when it propagates forward, and they will be attenuated toward when they propagate backward. The unidirectional mode converter has wide applications in nonlinearity induced isolation, mode insensitive element and on-chip mode locked laser.

Ferroresonance is one of the most harmful and longest known power quality disturbances in the history of AC power systems. The ability of predicting transient and steady-state ferroresonance simulations mainly depends on the accuracy of the power transformer model. Most existing voltage transformer models apply single-valued nonlinear functions to represent the core nonlinearities. This study, based on our previous work, proposes a newly improved and accurate transformer iron core hysteresis model for ferroresonance simulation by extension of the classical arctangent model. To verify the proposed model’s accuracy and superiority, three different ferroresonant voltage and current waveform simulations were performed using both the proposed model and renowned EMTP Type-96 model under the same system parameters. In addition, simulation results were compared with the corresponding experimental measurements. The results indicate that the proposed model is easily implemented using numerical modeling method with good stability and convergence, and is sufficiently accurate for both transient and steady-state periodic ferroresonance analysis.

Based on a new discrete Lax pair, an elementary explicit solution is found for the lattice sine-Gordon equation through Riemann surface method. It contains only exponential functions, quite different from the usual higher genus solutions, expressed with complicated theta functions. The solutions to the associated models, the lattice potential MKdV equation and a special H3 equation are also discussed.

The response of an underdamped stochastic resonance (SR) with a new pining potential model of domain wall (DW) in ferromagnetic strips driven by additive Gaussian white noise to an additive weak harmonic forcing is investigated. We address that the new nonlinear system can be converted between bi-stable and mono-stable freely by tuning the system parameters. Analytical expressions of signal-to-noise ratio (SNR) of the bi-stable stage is obtained based on the linear response theory. In addition, another type of SR, which occurs when the system is mono-stable, is also reported with the intrinsic frequency derived analytically. The SR in mono-stable stage confirms to the typical physical resonance better with frequency-selection characteristic. Numerical simulation of both stages is carried out with outputs conforming to the theoretical derivation. Owing to the diversity of potential model, the new system possesses considerable merits for engineering applications.