Modern Physics Letters B

A configuration space method is developed for binding energy calculations of the lowest energy exciton complexes (trion, biexciton) in spatially confined quasi-1D semiconductor nanostructures such as nanowires and nanotubes. Quite generally, trions are shown to have greater binding energy in strongly confined structures with small reduced electron–hole masses. Biexcitons have greater binding energy in less confined structures with large reduced electron–hole masses. This results in a universal crossover behavior, whereby trions become less stable than biexcitons as the transverse size of the quasi-1D nanostructure increases. The method is also capable of evaluating binding energies for electron–hole complexes in quasi-2D semiconductors such as coupled quantum wells and bilayer van der Walls bound heterostructures with advanced optoelectronic properties.

Many animal groups, such as bird flocks, clearly present structural order and appear to move as a single coherent entity. In interest to understand the complex behavior of these systems, many models have been proposed and tested so far. The aim of this work is to study and discuss numerically the scaling behavior in the 2D non-equilibrium phase transitions in spontaneously ordered motion of self-propelled particles in the framework of Vicsek model. This model is an important tool to study the behavior of collective motion of live biological and physical organisms. The calculation of the scaling exponents is effected by using the scaling dynamic method. However, the time evolution of the particles velocity present two different regimes separated by a cross-over time which increases linearly with both applied noise and radius of repulsive zone, but it decreases exponentially with the radius of orientation zone. The results show that the obtained exponents are similar to the growth and roughness ones used in the interfaces growth and to the submonolayer deposition process. The obtained values of these exponents are not dependent on the noises value, which proves their universality characters. Hence the kinetic evolution of the spontaneously ordered motion of self-propelled particles is self-similar. Implications of these findings are discussed.

In this paper, we investigate the steady-state properties and the transition rate for an ecological vegetation growth system induced by the terms of the colored multiplicative and additive noises. Numerical results indicate that the multiplicative noise and the additive one can reduce the stability of the ecological system and slow down the development velocity of the vegetation, while two noise self-correlation times can increase the stability of the system and speed up the expansion process of the vegetation system. With respect to the stochastic resonance (SR) phenomenon caused by noise terms and a multiplicative weak periodic signal, the results show that the additive noise always enhances the SR effect, two noise self-correlation time terms can produce SR phenomenon, but play opposite roles in enhancing or inhibiting the SR effect under different parameter conditions. In particular, the two self-correlation times can keep up the maximum of the signal-to-noise ratio (SNR) invariant in specific situations. Analogously, the multiplicative noise can not only improve the SNR, but also restrain the SR phenomenon in different cases.

In this paper, two (3+1)-dimensional nonlinear evolution equations (NLEEs) are under investigation by employing the Hirota’s method and symbolic computation. We derive the bilinear form and bilinear Bäcklund transformation (BT) for the two NLEEs. Based on the bilinear form, we obtain the multi-soliton solutions for them. Furthermore, multi-soliton solutions in terms of Wronskian determinant for the first NLEE are constructed, whose validity is verified through direct substitution into the bilinear equations.

The composite of $(1-x){\mathrm{\text{BaTiO}}}_3$–$(x){\mathrm{\text{Li}}}_{0.5}{\mathrm{\text{Fe}}}_{2.5}{\mathrm{\text{O}}}_4(x=0.00,0.05,0.10,0.15)$ was prepared by mixing lithium ferrite and barium titanate. The samples were sintered at 1150${}^{\circ }$C for optimum parameters at chemical reaction between ferrite–ferroelectric interfaces. The presence of ferroelectric nature was detected by X-ray diffraction (XRD) and homogenous coarseness nature was confirmed by scanning electron microscope (SEM). Dielectric measurement for the samples show the superimposition behavior of both magnetic and electric phases in the composite samples. This fact was further supported by magnetic behavior from vibrating sample magnetometer (VSM) and polarization from PE loops. Magnetic measurements show the increase in coercivity and saturation magnetization with increase in ferrite content. PE loops suggests that coercivity increases initially and then decreases for rise in ferrite content suggesting the trend of leaking factor in the samples.

In this paper, a fifth-order variable-coefficient nonlinear Schrödinger equation is investigated, which describes the propagation of the attosecond pulses in an optical fiber. Via the Hirota’s method and auxiliary functions, bilinear forms and dark one-, two- and three-soliton solutions are obtained. Propagation and interaction of the solitons are discussed graphically: We observe that the solitonic velocities are only related to ${\beta }_1(x)$, ${\beta }_2(x)$, ${\beta }_3(x)$ and ${\beta }_4(x)$, the coefficients of the second-, third-, fourth- and fifth-order terms, respectively, with $x$ being the scaled distance, while the solitonic amplitudes are related to ${\beta }_1(x)$, ${\beta }_2(x)$, ${\beta }_3(x)$, ${\beta }_4(x)$ as well as the wave number. When ${\beta }_1(x)$, ${\beta }_2(x)$, ${\beta }_3(x)$ and ${\beta }_4(x)$ are the constants, or the linear, quadratic and trigonometric functions of $x$, we obtain the linear, parabolic, cubic and periodic dark solitons, respectively. Interactions between (among) the two (three) solitons are depicted, which can be regarded to be elastic because the solitonic amplitudes remain unchanged except for some phase shifts after each interaction in an optical fiber.

Titanium dioxide (TiO₂) film was deposited by the direct current pulse magnetron sputtering technique. Then the surface of TiO₂ film was implanted by the N ion beam at room temperature. Through this way, N-doped TiO₂ (N–TiO₂) film was obtained and the band gap of N–TiO₂ film was decreased to 2.97 eV. XPS result revealed that N ion was doped into TiO₂ film as Ti–N and Ti–NO bonds. N ion was substitutionally/interstitially doped into TiO₂ crystal lattice and Ti–N bond was formed. N ion was doped into amorphous TiO₂ and Ti–ON bond was formed. The polycrystal TiO₂ film could result in that more N ion was substitutionally/interstitially doped into TiO₂ crystal lattice, which could effectively narrow the band gap of N–TiO₂ film. This work provides a potential N doping method which could be applied commercially.

This paper is an extension of the brief study by Sarah Douglas et al. [Phys. Plasmas 20 (2013) 114504] where in the study a sinusoidal perturbation of the heating power has been studied. In this paper a stepwise increase of the heating power and its influence on the $L$–$H$ transition are studied. Using a function, $Atanh(t/T)$ for the transition of input heating power for tokamak plasmas, i.e. the addition of the perturbation, $Atanh(t/T)$, to constant power $q_0$ is shown to promote the confinement, leading to the $L$–$H$ transition at a lower value of $q_0$, as compared to the case of constant $q_0$ without the $Atanh(t/T)$ perturbation. It is seen that the input heating power $Q$ that consists of constant part $q_0$ in addition to a function $Atanh(t/T)$ provides the $L$–$H$ transition for relatively small $A$ and much wider range values of $1/T$ as compared to Sarah Douglas et al. [Phys. Plasmas 20 (2013) 114504].

Chiral dielectrics are considered from the perspective of continuum representations of spatial heterogeneity. Static effects in isotropic chiral dielectrics are predicted, provided the electric field has nonzero third spatial derivatives. The effects are compared with static chiral phenomena in Cosserat elastic materials which obey generalized continuum constitutive equations. Dynamic monopole-like magnetic induction is predicted in chiral dielectric media.

Quantum information processing experimentally depends on optical-electronic devices. In this paper, we consider quantized mesoscopic RLC (resistance, inductance and capacitance) electric circuit in stable case as a quantum statistical ensemble, and calculate energy distribution (i.e. the energy stored in inductance and capacitance as well as the energy consumed on the resistance). For this aim, we employ the technique of integration within ordered product (IWOP) of operator to derive the thermo-vacuum state for this mesoscopic system, with which ensemble average energy calculation is replaced by evaluating expected value in pure state. This approach is concise and the result we deduced is physically appealling.