International Journal of Modern Physics B

We exclusively analyze the onset and condition of formation of modulated waves in a diffusive FitzHugh–Nagumo model for myocardial cell excitations. The cells are connected through gap junction coupling. An additive magnetic flux variable is used to describe the effect of electromagnetic induction, while electromagnetic radiation is imposed on the magnetic flux variable as a periodic forcing. We used the discrete multiple scale expansion and obtained, from the model equations, a single differential-difference amplitude nonlinear equation. We performed the linear stability analysis of this equation and found that instability features are importantly influenced by the induced electromagnetic gain. We present the unstable and stable regions of modulational instability (MI). The resulting analytic predictions are confirmed by numerical experiments of the generic equations. The results reveal that due to MI, an initial steady state that consisted of a plane wave with low amplitude evolves into a modulated localized wave patterns, soliton-like in shape, with features of synchronization. Furthermore, the formation of periodic pulse train with breathing motion presents a disappearing pattern in the presence of electromagnetic radiation. This could provide guidance and better understanding of sudden heart failure exposed to heavily electromagnetic radiation.

Semi-supervised community detection is an important research topic in the field of complex network, which incorporates prior knowledge and topology to guide the community detection process. However, most of the previous work ignores the impact of the noise from prior knowledge during the community detection process. This paper proposes a novel strategy to identify and remove the noise from prior knowledge based on harmonic function, so as to make use of prior knowledge more efficiently. Finally, this strategy is applied to three state-of-the-art semi-supervised community detection methods. A series of experiments on both real and artificial networks demonstrate that the accuracy of semi-supervised community detection approach can be further improved.

The ab-initio calculations based on the density functional theory (DFT) have been performed to study the structural, mechanical, electronic, thermal and thermodynamic properties of Al₃Sc and Al₃Ti binary compounds and their ternary mixture Al₃(Sc${}_{1-x}$Ti${}_x$) in L1₂ and D0${}_{22}$ structures. The total energy calculations show that the L1₂ structure is the more stable one. The Al₃Sc${}_{0.25}$Ti${}_{0.75}$ undergoes a martensitic transformation and the formation enthalpies and the lattice parameters decrease with increasing concentration x. The elastic constants are determined and the results show that all compounds are mechanically stable and the cubic cells are more easily deformed by shearing than by unidirectional compression. The elastic modulus indicates that the addition of Ti atoms to Al₃Sc improves its ductility. The densities of states (DOSs) calculations show the strong spd hybridization which leads to the formation of a pseudo-gap near the Fermi level in ternary alloys. The densities of states at the Fermi level N(E${}_F$) confirm the phase stability. The quasi-harmonic Debye model is used to predict the thermal properties such as heat capacity, Debye temperature, Grüneisen parameter and thermal expansion coefficient of the considered alloys. The determination of Gibbs free mixing energy at different concentrations has been used to calculate the T–x diagram.

In the present work, first-principles calculations were performed to obtain the structural, electronic and optical properties of lithium niobate crystal using two exchange-correlation functionals (GGA-PBE and TB-mBJ). The calculated structural parameters were very close to the experimental values. TB-mBJ functional was found to be good when compared to LDA and GGA functionals in case of bandgap energy of 3.715 eV of lithium niobate. It was observed that the upper valence and lower conduction bands consist mainly the O-2p and Nb-4$d$ states, respectively. Furthermore, calculations for real and imaginary parts of frequency-dependent dielectric function $𝜀(\omega )$ of lithium niobate crystal were performed using TD-DFT method. The ordinary refractive index n${}_o(\omega )$, extraordinary refractive index n${}_e(\omega )$, its birefringence and absorption peaks in imaginary dielectric function ${𝜀}_2(\omega )$ were also calculated.

The phonon, elastic and thermodynamic properties of L1₂ phase Rh₃Ta have been investigated by the density functional theory (DFT) approach combined with the quasi-harmonic approximation model. The results of the phonon band structure show that L1₂ phase Rh₃Ta possesses dynamical stability in the pressure range from 0–80 GPa due to the absence of imaginary frequencies. The pressure dependences with the elastic constants C${}_{ij}$, shear modulus G, bulk modulus B, Young’s modulus Y, Poisson’s ratio and B/G ratio have been analyzed. The results of the elastic properties studies show that L1₂ phase Rh₃Ta compound is mechanically stable and possesses a higher hardness, improved ductility and plasticity under higher pressures. The pressure and temperature relationship of the thermodynamic properties, such as the Debye temperature ${\mathrm{\Theta }}_D$, heat capacity C${}_p$, thermal expansion coefficient $\alpha$ and the Grüneisen parameter $\gamma$ are predicted by the quasi-harmonic Debye model in a wide pressure (0–80 GPa) and temperature (0–750 K) ranges.

Ion implantation is widely utilized in microelectromechanical systems (MEMS), applied for embedded lead, resistors, conductivity modifications and so forth. In order to achieve an expected device, the principle of ion implantation must be carefully examined. The elementary theory of ion implantation including implantation mechanism, projectile range and implantation-caused damage in the target were studied, which can be regarded as the guidance of ion implantation in MEMS device design and fabrication. Critical factors including implantations dose, energy and annealing conditions are examined by simulations and experiments. The implantation dose mainly determines the dopant concentration in the target substrate. The implantation energy is the key factor of the depth of the dopant elements. The annealing time mainly affects the repair degree of lattice damage and thus the activated elements’ ratio. These factors all together contribute to ions’ behavior in the substrates and characters of the devices. The results can be referred to in the MEMS design, especially piezoresistive devices.

In this paper, a multi-scale modeling approach is used to study the effect of adding graphene sheets to concrete matrix on the thermal conductivity of the concrete. By computing the thermal conductivity of the graphene along the armchair and zigzag directions using molecular dynamics (MO) simulations, it is shown that the graphene sheets have orthotropic thermal behavior. Therefore, at the upper scale, in which the finite element (FE) method is used to obtain the thermal conductivity of the concrete/graphene nanocomposites, the graphene sheets are considered as orthotropic continuous sheets. It is shown that the improvement of the concrete thermal conductivity by adding the graphene sheets is directly related to the graphene sheet volume percentage and cross-sectional dimensions.

Nanocrystalline Co${}_{0.5-x}$Zn${}_{0.5}$Cu${}_x$Fe₂O₄ spinel ferrites were prepared by autocombustion method with citric acid as fuel. Paramagnetic divalent copper ions substituted in place of ferromagnetic cobalt ions resulted in the modifications of structural and magnetic properties of the system. All samples were characterized with X-ray diffraction technique for structure determination. Crystallite sizes were calculated using Williamson–Hall plot and size–strain plots. Cation distribution and all other structural parameters were presented. Transmission electron microscopy measurements were done for x = 0 and x = 0.15 and they showed well-developed spherical particles with average sizes of 35 nm and 48 nm. Morphological studies were performed and grain growth was observed to be increased with copper concentration. EDAX measurements revealed the stoichiometric proportions of the samples as per the chemical composition. Mid-IR spectroscopy was used to characterize the spinel phase and displayed two characteristic absorption bands in all samples with a slight shift. M–H loops were recorded using vibrating sample magnetometer at room-temperature and highest saturation magnetization was observed to be 50.2 emu/g for the base (x = 0) sample. Magnetocrystalline anisotropy was discussed with the help of magnetocrystalline anisotropy constant K₁.

In this paper, the synchronization between spatially distributed power plants and their supported consumers is studied, where the case of Kuramoto-like model power grids connected to an external permanent magnet synchronous motor (PMSM) is taken as an example. We focus on the dependence of the synchronization on the coupling coefficient. To quantitatively study the synchronization degree, we introduce the order parameter and the frequency deviation to measure the synchronization of the coupled system. It is found that as the external coupling coefficient is increased, the distributed power grids and the loading system become more and more synchronized in space, and the complete synchronization appears at a particular value of external coupling coefficient. Our results may provide a useful tip for analyzing the synchronous ability of distributed power grids.

Stability of urban subway systems is a crucial issue in daily operation. This paper proposes a node failing process to test the stability of subway network by structure-based and flow-based node evaluation indicators. Furthermore, three network evaluation indicators are used to measure the network performance. The average transfer number of times (ATT) that is strongly associated with network structure and passenger flow will be discussed specifically. The results show that removing nodes with large inbound passenger flow cannot effectively damage the subway network structure, but it can result in significant increment of the ATT in the whole network. Another finding is that the ATT is smaller in peak hours compared with off-peak hours.

In this study, we propose a new bilayer-laminated magnetoelectric (ME) composite consisting of magnetostrictive Ni and Tb${}_{0.3}$Dy${}_{0.7}$Fe₂ (Terfenol-D) plates and piezoelectric Pb(Zr,Ti)O₃ (PZT) plate. The Ni–Terfenol–D-Ni/PZT composite is constructed and compared with the traditional Terfenol-D/PZT composite. The bias magnetic field and the electric field frequency dependences of the converse ME (CME) coefficient were investigated. It is shown that the Ni–Terfenol-D–Ni/PZT exhibits a large CME coefficient of 6.2 × 10${}^{-7}$ s/m at the electric field frequency of 42 kHz under a low bias magnetic field of 230 Oe, which results from the highly concentrated flux induced by Ni and the stress-interaction between Ni and magnetostrictive Terfenol-D.

This paper introduces a device performance optimization approach for the FinFET through optimization of the gate length. As a result of reducing the gate length, the leakage current (I${}_{\mathrm{\text{off}}}$) increases, and consequently, the stress along the channel enhances which leads to an increase in the drive current (I${}_{\mathrm{\text{sat}}}$) of the PMOS. In order to sustain I${}_{\mathrm{\text{off}}}$, work function is adjusted to offset the effect of the increased stress. Changing the gate length of the transistor yields different drive currents when the leakage current is fixed by adjusting the work function. For a given device, an optimal gate length is found to provide the highest drive current. As an example, for a standard performance device with I${}_{\mathrm{\text{off}}}$ = 1 nA/um, the best performance I${}_{\mathrm{\text{sat}}}$ = 856 uA/um is at L = 34 nm for 14 nm FinFET and I${}_{\mathrm{\text{sat}}}$ = 1130 uA/um at L = 21 nm for 7 nm FinFET. A 7 nm FinFET will exhibit performance boost of 32% comparing with 14 nm FinFET. However, applying the same method to a 5 nm FinFET, the performance boosting is out of expectance comparing to the 7 nm FinFET, which is due to the severe short-channel-effect and the exhausted channel stress in the FinFET.

The high-pressure strength of molybdenum (Mo) to 92 GPa has been studied by radial X-ray diffraction (RXRD) technique. The ratio of t/G is found to decrease above $\sim$24 GPa, showing the yield of Mo which is caused by plastic deformation at this pressure. Combined with high-pressure shear modulus, it was found that the differential stress corresponding to the yield of Mo at 24 GPa due to plastic deformation is 1.73 GPa. The second increase of t values occurs after $\sim$66 GPa, suggesting the strength of Mo with a differential stress of $\sim$1.93 GPa. In addition, the maximum difference stress of molybdenum at 87 GPa is 3.01 GPa.

Bandgap tailoring of $\beta$-Si₃N₄ is performed by single and co-doping by using density functional theory (DFT) of PBE functional and plane-wave pseudopotential method. The results reveal that a direct bandgap transfers into an indirect one when single-doped with As element. Also, a considerate decrease of bandgap to 0.221 eV and 0.315 eV is present for Al–P and As–P co-doped systems, respectively, exhibiting a representative semiconductor property that is characteristic for a narrower bandgap. Compared with other doped systems, Al-doped system with formation energy of 2.67 eV is present for a more stable structure. From charge density difference (CDD) maps, it is found that the blue area between co-doped atoms increases, illustrating an enhancement of covalent property for Al–P and Al–As bonds. Moreover, a slightly obvious “Blue shift” phenomenon can be obtained in Al, Al–P and Al–As doped systems, indicating an enhanced capacity of responses to light, which contributes to the insight for broader applications with regard to photoelectric devices.