Modern Physics Letters B

Motivated by ideas obtained from both ghost condensation and gravitational Higgs mechanism, we attempt to find classical solutions in the unitary gauge in general ghost condensation models. It is shown that depending on the form of scalar fields in an action, there are three kinds of exact solutions, which are (anti-) de Sitter space–time, polynomially expanding universes and flat Minkowski space–time. We briefly comment on gravitational Higgs mechanism in these models where we have massive gravitons of five degrees of freedom and one unitary scalar field (Nambu–Goldstone boson) after spontaneous symmetry breakdown of general coordinate reparametrization invariance. The models at hand are free from the problem associated with the non-unitary propagating mode.

An improved architecture, which performs a universal set of gates by current biasing of coupling Josephson junction, has been proposed. This improvement is necessary to the realization of a functional and scalable quantum computer. The proposed architecture is in line with current technology. Secondly, we investigate a scheme for implementing the Deutsch–Jozsa algorithm via the improved architecture. It is a simple, scalable and feasible scheme for the implementation of the Deutsch–Jozsa algorithm based on the current-controlled superconducting charge qubit network.

The purpose of this paper is to propose a theoretical approach, which can evaluate anharmonic effects on the rate constants within the transition state theory. In treating unimolecular reactions under collision-free conditions by using the RRKM theory, we make use of the inverse Laplace transformation of the partition functions to obtain both the total number of states for the activated complex and density of states for the reactant with the Morse oscillator potential. To demonstrate the applications of our theoretical approach, we choose some model systems and a real reaction as examples.

We introduce a new quantity, relevance-strength which describes the relevance of a node to the others in a scale-free network. We define a weight between two nodes i and j based on the shortest path length between them and the relevance-strength of a node is defined as the sum of the weights between it and others. For the Barabási and Albert model which is a well-known scale-free network model, we measure the relevance-strength of each node and study the correlations with other quantities, such as the degree, the mean degree of neighbors of a node, and the mean relevance-strength of neighbors. We find that the relevance-strength shows power law behaviors and the crossover behaviors for the degree and the mean relevance-strength of neighbors. Also, we study the scaling behaviors of the relevance-strength for various average relevance-strength for all nodes.

We demonstrate a double-clad Nd³⁺-doped polarization maintaining fiber (PMF) amplifier at 1064 nm for a compact configuration of a high-gain and low-noise optical fiber amplifier. The proposed 125 μm inner-cladding diameter in the double-clad fiber provides the single-mode propagation of the signal lightwave into its doped core without misguiding the signal lightwave into the outer-cladding. The small signal gain of Nd³⁺-doped fiber amplifier is 24 dB, and its noise coefficient is less than 8 dB.

By using the concept of negativity, we determine entanglement features of the tetrahedral lattice with Heisenberg interactions. It is found that except for the case of (1/2-1/2-1-1) mixed spins, there is no pairwise entanglement between any two spins at any temperature when B = 0. When B increases after B = 0, the ground-state negativities exhibit square wave or stepwise structures, and experience sharply descents to lower values at some energy-level crossing points. For thermal entanglement, the negativities exhibit ridge-like or staircase structures as B increases, and there are regions in the B–T plane where an increase of temperature may help to enhance the entanglement.

Cobalt thin films deposited by radio frequency sputtering were investigated. Microstructures of the Co films were analyzed by XRD and TEM. The results show that films microstructure varies with the variation of the sputter gas pressure P_Ar. Magnetic properties measured by VSM show that all the films possess relatively high saturation magnetization 4πM_s, and strong in-plane uniaxial magnetic anisotropy field H_k. Co films deposited below 0.3 Pa show soft magnetic properties and its microwave permeability was measured by vector network analyzer in the 0.1–5 GHz range.

Chignolin is an artificially designed ten-residue (GYDPETGTWG) folded peptide, which is the smallest protein and provides a good template for protein folding. In this work, we completed four explicit water molecular dynamics simulations of Chignolin folding using GROMOS and OPLS-AA force fields from extended initial states without any experiment informations. The four-folding free energy landscapes of the peptide has been drawn. The folded state of Chignolin has been successfully predicated based on the free energy landscapes. The four independent simulations gave similar results. (i) The four free energy landscapes have common characters. They are fairly smooth, barrierless, funnel-like and downhill without intermediate state, which consists with the experiment. (ii) The different extended initial structures converge at similar folded structures with the lowest free energy under GROMOS and OPLS-AA force fields. In the GROMOS force field, the backbone RMSD of the folded structures from the NMR native structure of Chignolin is only 0.114 nm, which is a stable structure in this force field. In the OPLS-AA force field, the similar results have been obtained. In addition, the smallest RMSD structure is in better agreement with the NMR native structure but unlikely stable in the force field.

The mean-field expressions derived from the transverse Ising model are used to investigate the second-order ferroelectric phase transition. With this theory, the properties of ferroelectric thin films formed by inserting a monolayer of material B into material A in the middle was studied. Firstly, a recursive equation for the phase transition properties of the ferroelectric thin film with one distinct inserting-layer in the middle was obtained. Next, the effect of the exchange interaction and transverse field parameters of materials A and B on the phase diagrams was investigated. The results show that with the modification of the parameter values of the inserting-layer B, the properties of the phase transition, the crossover value of the transverse field, the polarizations of different layers, and the critical temperature, change sensitively.

The present paper proposes a new empirical relationship to predict the values of volume dependence of the Gruneisen parameter. ε-Fe, NaCl, Li, Na and K in different pressure ranges have been employed to test the reliability of the model. The obtained results indicate that the model is reliable due to a good agreement between calculated results and the experimental data. Based on this modified model, the temperature dependence of thermal pressure for NaCl is also examined.

We have investigated the role of pinning density on the properties of the peak effect in the critical current density in superconducting systems. This study was conducted using a series of molecular dynamic simulations on two systems of nanostructures of periodic square arrays of pinning sites with different pining densities. We have found that the peak occurred in both systems only at zero temperature and for specific values of pinning strength. The most interesting result was that in both systems, the peak was found to occur only at nearly 0.5 fraction of the first matching field for all values of pinning strength. The properties of the peak were found to depend mainly on the initial positions of the vortices with respect to the positions of the pinning sites. The critical dipping force at the peak was found to increase linearly with the pinning strength and to have larger values for the system with the smaller density of pinning sites. The dependence of the relative height of the peak on the pinning strength was found be nearly the same in both systems. One-dimensional linear channels of moving vortices along the direction of the driving force were observed at the dip just before the peak.