International Journal of Modern Physics B

We consider a situation when observations can increase particle flow across a barrier by many orders of magnitude compared with the tunneling probability (a barrier anti-Zeno effect). It may be of interest for explaining the paradoxical results of experiments on “cold fusion” that has earlier been observed by other authors for various systems.

We examine the anti-Zeno effect in a model of a barrier of a special shape, which has similarities with the form of barriers to nuclear fusion in a solid, and moreover has an analytic solution. We have deducted formulas that demonstrate the conditions of increasing the barrier permeability.

Topological phase transitions of a two-dimensional topologically nontrivial polaritonic system are studied. A generic model of semiconductor excitons strongly coupled with tailored photonic modes is considered. We introduce a pseudospin operator, measuring the polariton polarization between photonic-like and excitonic-like. The associated pseudospin spectrum and pseudospin Chern numbers are calculated. It is shown that the pseudospin Chern number phase diagram exhibits certain features resembling the topological phase of quantum-spin-Hall-like. Moreover, a series of topological phase transitions may occur with the closing of the bulk energy gap or the pseudospin spectrum gap. In a tight-binding form, the edge-mode simulation is done numerically to confirm the analytically results.

The phase diagrams and magnetizations of an Ising nanowire with an amorphization are investigated by the use of the effective field theory with correlations. Some characteristic phenomena have been found in them. The reduced total magnetization falls below that of its corresponding crystalline ferromagnetic nanowire. The reentrant phenomena have been obtained, when the value of amorphization $\delta$ becomes larger than a critical value ($\delta =1.0$).

Based on density functional theory (DFT), the spin polarization properties of a thiophene molecule which is adsorbed at Fe (100) surface are discussed. A variety of horizontal and vertical adsorption configurations as well as their influences on the spin density distributions are studied in detail. The spin polarization comes from the $p$-$d$ orbital coupling between the thiophene molecule and the electrode, which leads to the molecules’ energy level shifting and the density of states (DOS) broadening, so the two spin states near the Fermi level are exchange split. It is also found that the interfacial spin polarization is different under different contact configurations, and the biggest one will be obtained when the S atom is directly placed above the Fe atom at the horizontal direction. On the other hand, interface spin inversion can be obtained by adjusting the adsorption position, which will be helpful to build spin sensors.

In this paper, we used a self-propelled particle model to study the transition between phases of collective behavior observed in animal aggregates. In these systems, transitions occur when individuals shift from one collective state to another. We investigated transitions induced by both the speed and the noise. Statistical quantities that characterize the phase transition driven by noise, such as order parameter, the Binder cumulant and the susceptibility were analyzed, and we used the finite-size scaling theory to estimate the critical exponent ratios $\beta /\nu$ and $\gamma /\nu$.

For research on the gravitational field routing mechanism on complex networks, we further analyze the gravitational effect of paths. In this study, we introduce the concept of path confidence degree to evaluate the unblocked reliability of paths that it takes the traffic state of all nodes on the path into account from the overall. On the basis of this, we propose an improved gravitational field routing protocol considering all the nodes’ gravities on the path and the path confidence degree. In order to evaluate the transmission performance of the routing strategy, an order parameter is introduced to measure the network throughput by the critical value of phase transition from a free-flow phase to a jammed phase, and the betweenness centrality is used to evaluate the transmission performance and traffic congestion of the network. Simulation results show that compared with the shortest-path routing strategy and the previous gravitational field routing strategy, the proposed algorithm improves the network throughput considerably and effectively balances the traffic load within the network, and all nodes in the network are utilized high efficiently. As long as $\gamma \ge \alpha$, the transmission performance can reach the maximum and remains unchanged for different $\alpha$ and $\gamma$, which ensures that the proposed routing protocol is high efficient and stable.

Pure and Gd-doped nano-crystalline GeSe₂ were prepared by the melt-quenching technique. Structure analysis using Rietveld program suggests monoclinic structure for both virgin and doped samples with nano-particle size 41 nm for GeSe₂ and 48 nm for Gd-doped sample. A wide optical band gap as estimated from absorbance measurements is 4.1 and 4.8 eV for pure and doped samples in accordance with the confinement effects. Raman spectra show two unresolved components at $\sim$202 cm${}^{-1}$ with broad line width. Also, well identified low intensity ($\upsilon$ $<$ 145 cm${}^{-1}$) and high intensity ($\upsilon$ $>$ 250 cm${}^{-1}$) bands are detected. For Gd-doped sample, the main band is shifted to lower energies and its full width at half maximum (FWHM) is reduced by $\sim$50% accompanied by an intensity increase of about $\sim$17 fold times. The photoluminescence analysis of the pure sample shows a main emission band at $\sim$604 nm. This band is split into two separated bands with higher intensity. The detected emission bands at wavelength $>$650 nm are assigned to transmission from ⁶G${}_{\mathrm{\text{J}}}$ to the different ⁶P${}_{\mathrm{\text{J}}}$ terms.

The Ba₃V₂O₈ and Ba₃V₂O₈:Eu${}^{3+}$ microflowers were synthesized by the composite-hydroxide-mediated (CHM) method from V₂O₅, BaCl₂ and Eu(NO${}_3{)}_3$ without using any surface-capping agent. XRD, EDS and XPS spectra of the crystals indicated that Eu${}^{3+}$ ions were incorporated into the Ba₃V₂O₈ lattices. The effect of doping Eu${}^{3+}$ on the magnetic property of Ba₃V₂O₈ crystal has been investigated at room temperature. The Ba₃V₂O₈:Eu${}^{3+}$ crystals exhibited room-temperature ferromagnetic behavior with remanence magnetization (Mr) of about 5.411 × 10${}^{-3}$ emu/g and coercivity (Hc) of 28.29 Oe. The mechanism of enhanced magnetic property of Eu-doped Ba₃V₂O₈ crystals has been discussed in detail.

Properties of interfaces of a phosphorene monolayer with six different low-index metal surfaces are calculated using density functional methods. Pd(111), Pd(110), Pd(100), Ti(0001), Au(110) and Ni(110) surfaces have been considered as these metals have been used as electrodes in experimental studies of phosphorene-based field effect transistor (FET) devices. In order to understand the chemistry of metal–phosphorene bonding, adsorption of individual atoms of these four metals on a phosphorene monolayer has also been studied. In addition to structural and electronic properties, barriers for charge injection at these metal–phosphorene interfaces have been studied by calculating the Schottky and tunneling barrier heights. Ti appears to be the best choice for metal electrode in phosphorene devices.

We address the behavior of Debye and Meissner masses of photons in a condensate of fermion pairs in the presence of number density asymmetry. Our formalism applies to a two-species fermionic system with number density asymmetry in BCS–Bose–Einstein condensation (BEC)–relativistic BEC crossover and with variable rapidity. Our results recover the known results of the photon self-energy in the ultrarelativistic limit and the superfluid density in the nonrelativistic limit. We further consider the electromagnetic stability of the condensate and show that the Meissner mass squared can become negative in the weakly coupling BCS regime and the strongly coupling relativistic BEC regime. The electromagnetic instability is compared to the mechanical stability discussed in previous works.

The structural, elastic and thermal properties of $\gamma$-TiAl and ${\alpha }_2$-Ti₃Al phases in the TiAl-based alloy under pressure were reported using CASTEP program based on the density functional theory. The calculated equilibrium parameters and elastic constants are in good agreement with experimental and the available theoretical data. The results indicate that under the same pressure, the ${\alpha }_2$ phase in the direction along $a$-axis is easier to be compressed than the $\gamma$ phase, while the compression along $c$-axis of $\gamma$ phase is larger than that of ${\alpha }_2$ phase; when the pressure is below 20 GPa, both the two phases are elastically stable, but the $\gamma$ phase have higher shear modulus and Young’s modulus, and the ${\alpha }_2$ phase has better ductility and plasticity. Debye temperature, bulk modulus, thermal expansion coefficient and heat capacity of the $\gamma$ phase and ${\alpha }_2$ phase under high pressure and high temperature were also successfully calculated and compared using the quasi-harmonic Debye model in the present work.

We have investigated the grain boundary energy of ($11\bar{2}1$) twin boundaries, the formation energies of hydrogen (H) and helium (He) defects in tetrahedral (T) and octahedral (O) interstitial sites at the ($11\bar{2}1$) twin boundary in hcp scandium (Sc) by first-principles calculations based on density functional theory. It is found that the formation energies of the tetrahedral and octahedral interstices H, and tetrahedral interstice He increase significantly towards the ($11\bar{2}1$) twin boundary plane, while the formation energy of the octahedral interstice He atom near the ($11\bar{2}1$) twin boundary plane decreases. To analyze these results, we present the electronic densities of states (DOSs) of H, He and their nearest-neighbor Sc (NN-Sc) atoms in several tetrahedral and octahedral configurations. We have also calculated the formation energies of He-vacancy clusters (He${}_n$V) in the Sc grain boundary, which indicates the stabilities of He${}_n$V clusters depend on the variations of the relaxed vacancy volume near the ($11\bar{2}1$) twin boundary plane.