Modern Physics Letters B

Information technology depends on how one can control and manipulate signals accurately and quickly. Transistors are at the core of modern technology and are based on electron charges. But as the device dimension shrinks, heating becomes a major problem. The spintronics explores the spin degree of electrons and thus bypasses the heat, at least in principle. For this reason, spin-based technology offers a possible solution. In this review, we survey some of the latest developments in all-optical switching (AOS), where ultrafast laser pulses are able to reverse spins from one direction to the other deterministically. But AOS only occurs in a special group of magnetic samples and within a narrow window of laser parameters. Some samples need multiple pulses to switch spins, while others need a single-shot pulse. To this end, there are several models available, but the underlying mechanism is still under debate. This review is different from other prior reviews in two aspects. First, we sacrifice the completeness of reviewing existing studies, while focusing on a limited set of experimental results that are highly reproducible in different labs and provide actual switched magnetic domain images. Second, we extract the common features from existing experiments that are critical to AOS, without favoring a particular switching mechanism. We emphasize that given the limited experimental data, it is really premature to identify a unified mechanism. We compare these features with our own model prediction, without resorting to a phenomenological scheme. We hope that this review serves the broad readership well.

In this paper, we consider the application of the ensemble Kalman filter for some nonlinear operator equations. According to the structural feature of the nonlinear operator, we construct an iteration process and the corresponding linear observation operator. This construction puts our problem into the frame of 3DVar. Based on the linear observation operator, the ensemble Kalman filter approach is adopted to blend the data into the dynamics to obtain an approximation of the unknown parameter. The method is applied to an inverse potential problem and a nonlinear Fredholm integral equation. The numerical results are compared with Bayesian approach, classical regularization methods including Tikhonov regularization and Landweber iteration, which shows that the proposed algorithm is effective and competitive.

In this paper, a (2+1)-dimensional generalized nonlinear Schrödinger equation is investigated, which is an important model in the field of optical fiber propagation. By employing the ansatz method, we obtain the bright soliton, dark soliton and complexiton of the equation. Some constraint conditions are also derived to ensure the existence of the solitons. Moreover, its power series solutions with the convergence analysis are also provided. Some graphical analyses of those solutions are presented in order to better understand their dynamical behavior.

In this paper, the nonlinear analysis of a viscous continuum traffic flow model is studied. The stability condition of the viscous continuum model is given by using the linear analysis method. The Korteweg–de Vries (KdV) equation is derived to describe the traffic jams. The effect of the viscous term is investigated by numerical simulations. The results show that the existence of the viscous term induces oscillation of traffic flow and the amplitude of the oscillation increases with increasing the coefficient of the viscous term. It is also found that the local clusters are compressed by increasing the coefficient of the viscous term.

We present our view in a standing debate about the definition and meaning of power-law entropies for continuous systems. Our suggestion is that such arguments should take into account the generalized operations of addition and multiplication induced by the power-law entropies’ composition properties. To be concrete, we highlight our view using the case of the “q-”, also known as “Tsallis”, entropic functionals.

In this paper, the mean first-passage time (MFPT) in simplified FitzHugh–Nagumo (FHN) neural model driven by correlated multiplicative non-Gaussian noise and additive Gaussian white noise is studied. Firstly, using the path integral approach and the unified colored-noise approximation (UCNA), the analytical expression of the stationary probability distribution (SPD) is derived, and the validity of the approximation method employed in the derivation is checked by performing numerical simulation. Secondly, the expression of the MFPT of the system is obtained by applying the definition and the steepest-descent method. Finally, the effects of the multiplicative noise intensity D, the additive noise intensity Q, the noise correlation time $\tau$, the cross-correlation strength $\lambda$ and the non-Gaussian noise deviation parameter q on the MFPT are discussed.

In this paper, a new semi-discrete coupled system which was firstly proposed by Bronsard and Pelinovsky is under investigation. Based on its known Lax pair, the infinitely-many conservation laws and discrete N-fold DT for this system are constructed. As applications, bell-shaped multi-soliton and breather solutions in terms of determinants for this system are firstly derived by means of the discrete N-fold DT. Propagation and elastic interaction structures of such soliton solutions are shown graphically: (1) Propagation characteristics of one-, two-, three- and four-soliton solutions are discussed from vanishing background. (2) Propagation characteristics of one- and two-breather solutions are analyzed from the plane wave background. The details of the dynamical evolutions for such soliton and breather solutions are studied via numerical simulations. Numerical results show the accuracy of our numerical scheme and the stable evolutions of these solitons with or without a noise in a relatively short period of time, while the evolutions exhibit obviously larger oscillations and strong instability with the increase in time. These results may be useful for understanding the propagation of orthogonally polarized optical waves in an isotropic medium and circularly polarized few-cycle pulses in Kerr media described by the coupled NLS and coupled complex mKdV equations, respectively.

In this paper, Riesz fractional coupled Schrödinger–KdV (SK) equations have been solved by implementing a new approach viz. time-splitting spectral method. In order to verify the results, it has also been solved by an implicit finite difference method by using fractional centered difference approximation for Riesz fractional derivative. The obtained results manifest that the proposed time-splitting spectral method is very effective and simple for obtaining approximate solutions of Riesz fractional coupled SK equations. In order to show the reliability and efficiency of the proposed methods, numerical solutions obtained by these methods have been presented graphically.

The crystalline and electronic structural properties of Zinc Telluride (ZnTe) are investigated systematically up to $\sim$25 GPa using a diamond anvil cell (DAC) in conjunction with a series of advanced optical and electrical testing methods at both non-hydrostatic and hydrostatic conditions. Based on Raman spectroscopy and AC impedance spectroscopy, ZnTe undergoes two phase transitions from initial zinc-blende phase to cinnabar phase at 7–9 GPa, then it transforms to Cmcm phase at 11–13 GPa under the non-hydrostatic condition. Meantime, the semiconductor to metal phase transition is verified by the temperature-dependent conductivity measurements. In these studies, the pressure points of phase transition and metallization of ZnTe are approximately same under the hydrostatic condition. The feeble influence of non-hydrostatic and hydrostatic conditions on the phase transition and metallization of ZnTe can be reasonably explained by its own crystalline structure from atomic force microscopy and high-resolution transmission electron microscopy.

Using a direct test function based on the Hirota’s bilinear form, two classes of mixed type exact solutions to the (2+1)-dimensional Ito equation are found through symbolic computations with Mathematica. These mixed type exact solutions contain exponential function, trigonometric function and hyperbolic function. The physical structures and characteristics for these resulting mixed type exact solutions are illustrated by some three-dimensional plots and contour plots.

A Toda lattice hierarchy is studied by introducing a new spectral problem which is a discrete counterpart of the generalized Kaup–Newell spectral problem. Based on the Lenard recursion equation, Lax pair of the hierarchy is given. Further, the discrete spectral problem is nonlinearized into an integrable symplectic map. As a result, an algebraic–geometric solution in Riemann theta function of the hierarchy is obtained. Besides, two equations, the Volterra lattice and a (2+1)-dimensional Burgers equation with a discrete variable, yielded from the hierarchy are also solved.

In this paper, the (3+1)-dimensional generalized Kadomtsev–Petviashvili (gKP) equation is discussed, which can be used to describe certain characteristics of soliton in a nonlinear media with weak dispersion. By using the virtue of Bell polynomial, we construct the exact bilinear formalism and soliton wave of the equation, respectively. We also analyze its stability analysis. Moreover, based on the resulting bilinear formalism, we obtain its rouge wave solutions with a direct method. Finally, we also discuss the interaction phenomena between solitary wave solutions and rogue wave solutions. It is hoped that our results can be used to enrich the dynamics of the (3+1)-dimensional nonlinear wave fields.

In this work, numerical calculations and simulation based on Transfer Matrix Method have been presented to investigate a model solar cell structure. New four-layered structure containing different types of semiconductor has been presented, analyzed and discussed. The average reflectance and average transmittance in the visible light are derived and plotted versus the operating wavelength at different physical parameters. The obtained results show that the proposed structure is a promising candidate to be used for designing future solar cell structures.

Borophene as a monolayer of boron atoms has been recently synthesized. Experimental reports show that the borophene can have different stable phases. In this paper, we study the effect of halogen atom adsorption on electrical and mechanical properties of ${\beta }_{12}$ borophene sheet using density functional theory. Adsorption of F, Cl, Br and I is considered and it is found that electronegativity and mass of halogen atom significantly affect the mechanical ability of the sheet. Young’s modulus of the sheet is decreased in the presence of halogen atoms. In addition, halogen atoms control electrical properties of the borophene sheet.