International Journal of Modern Physics B

Based on an improved neuronal model, in which the effect of magnetic flux is considered during the fluctuation and change of ion concentration in cells, the transition of synchronization is investigated by imposing external electromagnetic radiation on the coupled neurons, and networks, respectively. It is found that the synchronization degree depends on the coupling intensity and the intensity of external electromagnetic radiation. Indeed, appropriate intensity of electromagnetic radiation could be effective to realize intermittent synchronization, while stronger intensity of electromagnetic radiation can induce disorder of coupled neurons and network. Neurons show rhythm synchronization in the electrical activities by increasing the coupling intensity under electromagnetic radiation, and spatial patterns can be formed in the network under smaller factor of synchronization.

Based on first-principles plane-wave ultra-soft pseudopotential method, bandgaps of Ga${}_{1-x}$Al${}_x$N nanowires with different diameters and different Al constituents are calculated. After the optimization of the model, the bandgaps are achieved. According to the results, the bandgap of Ga${}_{1-x}$Al${}_x$N decreases with increasing diameter and finally, closed to that of the bulk. In addition, with increasing Al constituent, the bandgaps of Ga${}_{1-x}$Al${}_x$N nanowires increase. However, the amount of the increase is lower than that of the bulk Ga${}_{1-x}$Al${}_x$N with the increase of Al constituent.

We investigate electron transport between circular graphene quantum dots (CGQDs) and ZnO nanowires (ZnO NWs). This structure can be used as donor and acceptor in hybrid solar cells. We consider circular quantum dots (QDs) and use analytical calculation in order to estimate wavefunctions of GQD and ZnO NWs. After calculating the wavefunctions overlap, we use Marcus relation in order to calculate electron transfer rate. Also, we calculate this transfer rate for CdSe QDs–ZnO NWs system. Results from analytical calculation show that the transfer rate is limited to 10${}^{13}$ s${}^{-1}$. This result is in agreement with experimental results which are reported earlier. Such systems could be suitable for solar cells.

Many link prediction methods have been proposed for predicting the likelihood that a link exists between two nodes in complex networks. Among these methods, similarity indices are receiving close attention. Most similarity-based methods assume that the contribution of links with different topological structures is the same in the similarity calculations. This paper proposes a local weighted method, which weights the strength of connection between each pair of nodes. Based on the local weighted method, six local weighted similarity indices extended from unweighted similarity indices (including Common Neighbor (CN), Adamic-Adar (AA), Resource Allocation (RA), Salton, Jaccard and Local Path (LP) index) are proposed. Empirical study has shown that the local weighted method can significantly improve the prediction accuracy of these unweighted similarity indices and that in sparse and weakly clustered networks, the indices perform even better.

Structural, elastic, optical, and electronic properties of wurtzite (WZ), zinc-blende (ZB), and rocksalt (RS) structures of AlN are investigated using the first-principles method and within the framework of density functional theory (DFT). Lattice parameters, bulk modulus, shear modulus, Young’s modulus, and elastic constants are calculated at zero pressure and compared with other experimental and theoretical results. The wurtzite and zinc-blende structures have a transition to rocksalt phase at the pressures of 12.7 GPa and 14 GPa, respectively. The electronic properties are calculated using both GGA and EV-GGA approximations; the obtained results by EV-GGA approximation are in much better agreement with the available experimental data. The RS phase has the largest bandgap with an amount of 4.98 eV; by increasing pressure, this amount is also increased. The optical properties like dielectric function, energy loss function, refractive index, and extinction coefficient are calculated under pressure using GGA approximation. Inter-band transitions are investigated using the peaks of imaginary part of the dielectric function and these transitions mainly occur from N-2$p$ to Al-3$p$ levels. The results show that the RS structure has more different properties than the WZ and ZB structures.

Discord and entanglement characterize two kinds of quantum correlations, and discord captures more correlation than entanglement in the sense that even separable states may have nonzero discord. In this paper, we propose a new kind of quantum correlation that we call as oblique discord. A zero-discord state corresponds to an orthonormal basis, while a zero-oblique-discord state corresponds to a basis which is not necessarily orthogonal. Under this definition, the set of zero-discord states is properly contained inside the set of zero-oblique-discord states, and the set of zero-oblique-discord states is properly contained inside the set of separable states. We give a characterization of zero-oblique-discord states via quantum mapping, provide a geometric measure for oblique discord, and raise a conjecture, which if it holds, then we can define an information-theoretic measure for oblique discord. Also, we point out that the definition of oblique discord can be properly extended to some different versions just as the case of quantum discord.

A multifaceted experimental study of collisions of Na${}^{+}$ and K${}^{+}$ ions in the energy range of 0.5–10 keV with He and Ar atoms is presented. Absolute cross-sections for charge-exchange, ionization, stripping and excitation processes were measured using a refined version of the transfer electric field method, angle- and energy-dependent collection of product ions, energy loss and optical spectroscopy methods. The experimental data and the schematic correlation diagrams are employed to analyze and determine the mechanisms for these processes.

This work reports the influence of sintering temperature on structure, microstructure and piezoelectric properties of 0.48 Ba(Zr${}_{0.2}$Ti${}_{0.8}$)O₃–0.52 (Ba${}_{0.7}$Ca${}_{0.3}$)TiO₃(BZT–BCT) doped with ZnO nanoparticle ceramics manufactured by a conventional solid state reaction method. By increasing sintering temperature, the piezoelectric behaviors were improved and rose up to the best parameters at a sintering temperature of 1450${}^{\circ }$C ($d_{33}=576$ pC/N and $k_p=0.55$). The corresponding properties of undoped BZT–BCT ceramics were investigated as a comparison. The received results show that the sintering behavior and piezo-parameters of doped BZT–BCT samples are better than the undoped BZT–BCT samples at each sintering temperature.

An additional concave incident surface comprised of two-dimensional (2D) sonic crystals (SCs) is employed to tune the acoustic image in the far-field region. The tunability is realized through changing the curvature of the concave surface. To explain the tuning mechanism, a simple ray-trace analysis is demonstrated based on the wave-beam negative refractive law. Then, a numerical confirmation is carried out. Results show that both the position and the intensity of the image can be tuned by the introduced concave surface.

In this paper, we analyze the dynamics of the measurement-induced nonlocality (MIN) of two-qubit states undergoing decoherence induced by a structured environment modeled as a collection of simple harmonic oscillators. For the Markovian dynamics, MIN and the concurrence decrease monotonically with the scaled time and the decoherence time of the former is longer than that of the latter. While for the non-Markovian dynamics, MIN can revive for finite time periods after its disappearance immediately. With a comparison, the concurrence can revive for finite time periods after its complete disappearance which lasts for some time. The MIN takes a zero value for some discrete time points while the concurrence takes a zero value for finite time periods. In this sense, we can say that the MIN is more robust than the concurrence to decoherence. Finally, the non-Markovianity measure has been examined and we find that the strong non-Markovianity of the dynamical process corresponds to a large amplitude of the revival of MIN and the concurrence.

In the present paper, we report on the switching dynamics of both single and coupled VO₂-based oscillators, with resistive and capacitive coupling, and explore the capability of their application in oscillatory neural networks. Based on these results, we further select an adequate SPICE model to describe the modes of operation of coupled oscillator circuits. Physical mechanisms influencing the time of forward and reverse electrical switching, that determine the applicability limits of the proposed model, are identified. For the resistive coupling, it is shown that synchronization takes place at a certain value of the coupling resistance, though it is unstable and a synchronization failure occurs periodically. For the capacitive coupling, two synchronization modes, with weak and strong coupling, are found. The transition between these modes is accompanied by chaotic oscillations. A decrease in the width of the spectrum harmonics in the weak-coupling mode, and its increase in the strong-coupling one, is detected. The dependences of frequencies and phase differences of the coupled oscillatory circuits on the coupling capacitance are found. Examples of operation of coupled VO₂ oscillators as a central pattern generator are demonstrated.

The spin Hamiltonian parameters of VO${}^{2+}$ in KZnClSO${}_4\cdot$3H₂O single crystals are calculated from the third-order perturbation formulas based on the double spin–orbit coupling model for the tetragonal transition-ion clusters in crystals with the ground state $|d_{xy}〉$. In the paper, both the crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (double-mechanism model) are considered to calculate the spin Hamiltonian parameters. The calculated results are in agreement with the experimental data. Moreover, the calculated results show that the CT mechanism cannot be omitted for a high-valence state V${}^{4+}$ ions in KZnClSO${}_4\cdot$3H₂O single crystals. The tetragonal field parameters are also acquired in the paper.

Using first-principles calculation we investigated the structural, electronic and elastic properties of paramagnetic CaFeAs₂. Our results indicated that the density of states (DOS) was dominated predominantly by Fe-3$d$ states at Fermi levels, and stronger hybridization exists between As₁ and As₁ atoms. Three hole pockets are formed at $\mathrm{\Gamma }$ and Z points, and two electronic pockets are formed at A and E points. The Dirac cone-like bands appear near B and D points. For the first time we calculated the elastic properties and found that CaFeAs₂ is a mechanically stable and moderately hard material, it has elastic anisotropy and brittleness, which agrees well with the bonding picture and the calculation of Debye temperature (${\mathrm{\Theta }}_{\mathrm{\text{D}}}$).

Quantum key distribution (QKD) promises unconditionally secure communications, however, the low bit rate of QKD cannot meet the requirements of high-speed applications. Despite the many solutions that have been proposed in recent years, they are neither efficient to generate the secret keys nor compatible with other QKD systems. This paper, based on chaotic cryptography and middleware technology, proposes an efficient and universal QKD protocol that can be directly deployed on top of any existing QKD system without modifying the underlying QKD protocol and optical platform. It initially takes the bit string generated by the QKD system as input, periodically updates the chaotic system, and efficiently outputs the bit sequences. Theoretical analysis and simulation results demonstrate that our protocol can efficiently increase the bit rate of the QKD system as well as securely generate bit sequences with perfect statistical properties. Compared with the existing methods, our protocol is more efficient and universal, it can be rapidly deployed on the QKD system to increase the bit rate when the QKD system becomes the bottleneck of its communication system.