Modern Physics Letters B

We review recent progress in the nonequilibrium dynamics of thermally isolated many-body quantum systems, evolving with an ensemble of Hamiltonians as opposed to deterministic evolution with a single time-dependent Hamiltonian. Such questions arise in (i) quantum dynamics of disordered systems, where different realizations of disorder give rise to an ensemble of real-time quantum evolutions, (ii) quantum evolution with noisy Hamiltonians (temporal disorder), which leads to stochastic Schrödinger equations, and, (iii) in the broader context of quantum optimal control, where one needs to analyze an ensemble of permissible protocols in order to find one that optimizes a given figure of merit. The theme of ensemble quantum evolution appears in several emerging new directions in noneqilibrium quantum dynamics of thermally isolated many-body systems, which include many-body localization, noise-driven systems, and shortcuts to adiabaticity.

The vibrational properties of nanoparticles coupled with surrounding media are of recent interest. These nanostructures can be modeled as nanoscale spherical solids. In this paper, new formulation based on the nonlocal elasticity theory is proposed to investigate radial vibrations of the nanoparticles immersed in fluid medium. The nanoparticles with size ranging from 1 nm to 10 nm are discussed. The nanoparticles are considered elastic, homogeneous and anisotropic. Along the contact surface between the nanoparticle and the fluid, the compatibility requirement is applied and the Bessel functions are used to obtain the complex frequency equation. Numerical results are evaluated, and their comparisons are performed to confirm the validity and accuracy of the proposed method. Furthermore, the model is used to elucidate the effect of small scale on the vibration of several nanoparticles. Our results show that the small scale is essential for the radial vibration of nanoparticles when the nanoparticle radius is smaller than 2 nm.

Finding a universal method of crystal structure solution and proving the Riemann hypothesis are two outstanding challenges in apparently unrelated fields. For centro-symmetric crystals however, a connection arises as the result of a statistical approach to the inverse phase problem. It is shown that parameters of the phase distribution are related to the non-trivial Riemann zeros by a Mellin transform.

In this paper, we investigate theoretically a dilute stream of free quantum particles passing through a macroscopic circular aperture of matter-waves and then moving in a space at a finite temperature, taking into account the dissipative coupling with the environment. The portion of particles captured by the detection screen is studied by varying the distance between the aperture and the screen. Depending on the wavelength, the temperature, and the dimension of the aperture, an unusual local valley-peak structure is found in increasing the distance, in contrast to traditional thinking that it decreases monotonically. The underlying mechanism is the nonlocality in the process of decoherence for an individual particle.

In this paper, we propose a novel tunneling graphene nanoribbon field effect transistor by modification of the conventional structure in a way that its drain high-doped extension part is replaced by lightly linear doped region. Then the proposed structure has a Schottky contact at the drain side. As the source contact is ohmic and the drain contact is Schottky, this structure is called Schottky–Ohmic tunneling graphene nanoribbon field effect transistor. Electrical behaviors of the proposed device are investigated by mode space nonequilibrium Green's function (NEGF) formalism in the ballistic limit. Simulation results show that without increasing transistor length, I_OFF, I_ON/I_OFF, ambipolar behavior, delay time and PDP of the proposed structure improve, in comparison with the conventional tunneling graphene nanoribbon field effect transistor with the same dimension. Also subthreshold swing which is one of the evident characteristics of the tunneling FET is preserved in this structure.

In this paper, we consider an environmental interface as a complex system, in which difference equations for calculating the environmental interface temperature and deeper soil layer temperature are represented by the coupled maps. First equation has its background in the energy balance equation while the second one in the prognostic equation for deeper soil layer temperature, commonly used in land surface parametrization schemes. Nonlinear dynamical consideration of this coupled system includes: (i) examination of period one fixed point and (ii) bifurcation analysis. Focusing part of analysis is calculation of the Lyapunov exponent for a specific range of values of system parameters and discussion about domain of stability for this coupled system. Finally, we calculate Kolmogorov complexity of time series generated from the coupled system.

The statistical moment method has been used to study the effect of isotopic mass difference on extended X-ray absorption fine structure (EXAFS) Debye–Waller factor of crystalline germanium. The effects on the parallel mean-square relative displacement and the atomic mean square displacements have been considered. This research also exposed that isotopic effect is noticeable where the correlated atomic motion is concerned. Numerical calculations have been performed for two isotopes ⁷⁰Ge and ⁷⁶Ge in range of temperature from 0 K to 600 K. Our results are compared with available experimental EXAFS data [J. Purans et al., Phys. Rev. Lett.100 (2008) 055901] as well as with lattice dynamics calculations [A. Sanson, Solid State Sci.12 (2010) 1988] and the good agreements are found.

In this paper, a series of rare-earth-doped barium hexaferrite powders (Ba_0.95Re_0.05-Fe₁₂O₁₉ and Ba_0.95Re_0.05M_0.05Fe_11.95O₁₉: Re = La, Pr, Sm, Nd, Gd, Dy, Yb; M = Zn²⁺, Mn²⁺, ) were synthesized by the sol–gel self-combustion technology. The phase composition and the magnetic properties of the as-prepared barium hexaferrites were characterized and discussed with X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that the barium hexaferrites exhibited the magnetoplumbite phase structure with the average diameter of 45 nm. Magnetic properties study revealed that the variation of the saturation magnetization (M_s) was similar with the change of the rare-earth ions radius, but the change of M_s was low. This indicated that the magnetic moments of rare-earth ions could not affect M_s. The magnetocrystalline anisotropy field mainly influenced the anisotropism of hexaferrites, and the coercivity (H_c) of the rare-earth ions doped barium hexaferrites basically decreased with the increasing orbital quantum numbers (except Sm³⁺ and Gd³⁺). Further study showed the co-addition of Zn²⁺ and Mn²⁺ did not change the trend of M_s and H_c. Thus, it is concluded that the rare-earth ions played an important role for the anisotropy field of barium hexaferrites.