International Journal of Modern Physics B

The structural and dynamical properties in sodium silicate liquid were investigated by molecular dynamics method. To clarify the distribution of sodium atoms in model, characteristics of simplex have been investigated. The simulation results reveal that Na₂O⋅4SiO₂ (NS₄) liquid has a lot of simplexes with four sodium atoms inside but about half of simplexes do not have sodium. The spatial distribution of sodium is nonuniform, sodium tends to be in the nonbridging oxygen-simplexes and in larger-radius simplex. Moreover, the sodium density for nonbridging oxygen region is significantly higher than the one for Si-region. Namely, link-cluster function F${}_{lk}$(r, t) has been used to clarify dynamical heterogeneity in NS₄ liquid. The F${}_{lk}$(r, t) for sets of random, immobile and mobile network atoms is quite different, which indicates that the dynamics of network atoms is heterogeneous. The Si–O network has the structure with two separated domains (immobile and mobile domains). These types of domain are significantly different in local microstructure, mobility of atoms and chemical composition.

Rheological properties of Cholesteryl n-valerate, Cholesteryl decanoate and Cholesteryl myristate which are esters of cholesterol have been studied. Phase transition temperatures and rheological parameters such as viscosity, elastic modulus G${}^{\prime }$, loss modulus G${}^{″}$ as functions of temperature, shear rate and time are investigated. In frequency sweep test, a higher transition crossover region has occurred for Cholesteryl myristate, whereas for Cholesteryl n-valerate a frequency-independent plateau prevailed for both the moduli. The occurrence of blue phase in Cholesteryl decanoate during temperature sweep measurements is an indication for the rheological support. The results for steady state have informed that cholesteric esters are having non-Newtonian flow behavior in their respective cholesteric phases. The power-law model has explained well the shear rate dependence of shear stress. A few practical applications of these esters as lubricant additives are discussed, too.

The complex Ginzburg–Landau equation (CGLE) is used to investigate the effect of a nonlocal feedback control on spiral dynamics in oscillatory media, where the feedback is derived from a square-shaped domain, and three kinds of controlled tip trajectories can be found. The tip trajectory usually tends to a square limit cycle concentric with the measuring domain when the initial tip location is near the periphery of the domain. If the spiral tip is initially located in the measuring domain, it will finally be fixed at a point in the domain. For some larger delay time, the spiral tip may have a motion pathway of small limit cycles. For the case of a square-shaped pathway, the modulus function of the feedback signal has a maximum value when the spiral tip approaches the midpoint of each side, and a slower change when the tip is close to each turning point. As the feedback gain is increased, the spiral tip moves along the same pathway with a greater speed, and multiple tips can be generated when the gain is very large. The final trajectory is also affected by the distance between the measuring center and the initial spiral tip, the size of the measuring domain, the delay time, the choice of positive and negative gains and the scaling parameter.

We select the asymmetric Gaussian (AG) and the parabolic (P) confinement to describe the along growth direction and perpendicular to growth direction confinement potential (CP) of an electron in a disk-like quantum dot (QD), respectively. Using the Pekar-type variational (PTV) method, we investigate the eigenenergies of the ground and first-excited states (GFES) of the polaron in the QD, changing the QD dimensions. We study the hydrogen-like impurity (HLI) and the polarization effect. Our numerical results show the influence of the QD dimensions on the mean number of phonons, energies, transition frequency and probability. The Coulomb potential of hydrogen-like impurity and the polarization effect of the medium cannot be ignored. We find that the electric field is an indispensable condition for the induced polaron transition. The weak electric field has a strong regulatory function on the transition. AG confinement is more drastic than P confinement in modulating polaron transition properties. This work confirms that the choice of a CP is crucial for the study of polaron transition in nanostructures. This quantum system can be employed as a two-level quantum qubit.

The difficulty of recycling and low photocatalytic efficiency in the visible light significantly limit the use of nano-TiO₂ in water pollution control. In this work, Bucky papers (BPs), which play a vital role for adsorption of pollutants and transfer of electrons, are introduced as substrates to fabricate and anchor TiO₂ nanorods by a facile hydrothermal method. The photocatalytic properties of the TiO₂ and BP composites (TiO₂@BP) are studied by photodegrading methylene blue in water solutions. It is found that TiO₂@BP possesses four times photocatalytic efficiency for methylene blue of TiO₂@Si under ultraviolet light irradiation and 10 times under visible light irradiation. This is considered to be attributed to the synergic effect of TiO₂@BP system and surface defects of TiO₂ nanorods. The TiO₂@BP also shows a stable photocatalytic property even after five cyclic photocatalytic degradation. This study indicates that TiO₂@BP is a promising candidate for photocatalytic applications, which provides a reference for further research on synthesis of reusable photocatalysts with higher efficiency.

Quantum and noncommutative corrections to the Newtonian law of inertia are considered in the general setting of Verlinde’s entropic force postulate. We demonstrate that the form for the modified Newtonian dynamics (MOND) emerges in a classical setting by seeking appropriate corrections in the entropy. We estimate the correction term by using concrete coherent states in the standard and generalized versions of Heisenberg’s uncertainty principle. Using Jackiw’s direct and analytic method, we compute the explicit wavefunctions for these states, producing minimal length as well as minimal products. Subsequently, we derive a further selection criterium restricting the free parameters in the model in providing a canonical formulation of the quantum corrected Newtonian law by setting up the Lagrangian and Hamiltonian for the system.

In this study, based on the Hirota bilinear method, mixed lump-solitons, periodic lump and breather soliton solutions are derived for (2 + 1)-dimensional extended KP equation with the aid of symbolic computation. Furthermore, dynamics of these solutions are explained with 3d plots and 2d contour plots by taking special choices of the involved parameters. Through the mixed lump-soliton solutions, we observe two fusion phenomena, first from interaction of lump and single soliton and other from interaction of lump with two solitons. In both cases, lump moves gradually towards soliton and transfers energy until it completely merges with the solitons. We also observe new characteristics of periodic lump solutions and kinky breather solitons.

To choose an ideal method to study the phonon properties of graphene, the results of thermal conductivity (TC) of graphene computed using the equilibrium molecular dynamics (EMD), reverse nonequilibrium molecular dynamics (RNEMD) and direct nonequilibrium molecular dynamics (DNEMD) with Tersoff potential are compared, and we find that all of them are very close to each other. While two of them have been compared in the past, there is a lack of comparison of the three methods. Eventually, we choose the Green–Kubo method to study the temperature dependence of TC in graphene and find that the $\kappa$ diverges with the system temperature T as $\kappa \backsim$T${}^{\alpha }$ with $\alpha =-0.58$ and $\alpha =-0.61$ for the direction of armchair and zigzag, respectively, which is in reasonable agreement with the one in recent theoretical and experimental researches. To gain further insight into the TC, the phonon dispersion and the phonon density of states (PDOS), which depend on evaluating the eigenvalues and the eigenvectors of dynamical matrix, are calculated for graphene with dimensions of 30 × 30 unit cell by a combination of EMD simulations and lattice dynamics calculations.

An evolution equation is introduced which governs a two-sided optical cavity under spontaneous photon emission. This equation implies a system of rate equations for expectation values of combinations of operators relevant to the cavity. This system of equations closes with respect to these variables and it can be solved completely in closed form. Some of the properties of the solutions such as the large time behavior of the expectation values and other properties will be discussed.

The multiferroic magnetoelectric materials have gained intensive research interest in the recent years due to their prospective applications. In this perspective, the thermally tunable complex impedance, dielectric behavior and room-temperature magnetoelectric coupling of xCo${}_{0.5}$Ni${}_{0.5}$Fe₂O₄–(1 - x)PbZr${}_{0.58}$Ti${}_{0.42}$O₃ (x = 0.2, 0.3 and 0.5) nanocomposites have been investigated. A series of samples have been prepared by chemical pyrophoric reaction process. The structural characterization confirms the coexistence of two different types of phases, there is no phase segregation. The temperature-controlled complex impedance analysis reveals that grain boundaries and grain of the nanocomposites are playing a dominating role. The existence of Maxwell–Wagner interfacial polarization of the nanocomposites causes a high dielectric constant at low frequency. The calculated AC conductivity values with frequency at different temperatures follow the Jonscher’s power-law. A small polaronic hopping contributes largely to the conduction process of the decorated composite. The magnetostriction properties lead to the AC and DC magnetic field-dependent magnetoelectric coupling of the nanocomposites. The magnetoelectric coupling coefficient depends on the concentration of the piezomagnetic phase of the composites.

In this paper, we define a class of weighted directed networks with the weight of its edge dominated by a weight parameter w. According to the construction of the networks, we study two types of random walks in the weighted directed networks with a trap fixed on the central node, i.e., standard random walks and mixed random walks. For the standard random walks, the trapping process is controlled by a weight parameter w which changes the transition probability of random walks. For the mixed random walks including nonnearest-neighbor hopping, the trapping process is steered by a stochastic parameter $𝜃$, where $𝜃$ changes the walking rule. For the above two techniques, we derive both analytically the average trapping time (ATT) as the measure of trapping efficiency, and the obtained analytical expressions are in good agreement with the corresponding numerical solutions for different values of w and $𝜃$. The obtained results indicate that ATT scales superlinearly with network size N_n and the weight parameter w changes simultaneously the prefactor and the leading scalings of ATT, while the stochastic parameter $𝜃$ can only alter the prefactor of ATT and leave the leading scalings of ATT unchanged. This work may help in paving the way for understanding the effects of the link weight and nonnearest-neighbor hopping in real complex systems.

In this study, zinc selenide (ZnSe) thin films were produced on glass substrate by using chemical bath deposition (CBD) method at 80${}^{\circ }$C, from aqueous solutions of zinc sulphate and sodium selenosulphide, which were produced using solid selenium as the selenium source. The optical and structural properties of ZnSe thin films were investigated at room-temperature. The pH of the chemical bath, in which ZnSe thin films were immersed, were changed between pH:8–11. Optical properties of the films, including extinction coefficient, refractive index, reflectance, absorbance, transmittance, dielectric constants and optical density values were calculated using absorbance and transmittance measurements determined using a Hach Lange 500 spectrophotometer, in 300–1100 nm wavelength range. Optical bandgap values were obtained from transmittance and absorbance spectra ranged between 2.12 and 2.49 eV. According to XRD results, it was found that the films have polycrystalline structure and they exhibited different film thicknesses depending on phase and pH changes.