International Journal of Modern Physics B

Looking for a handy and exact calculation for the equivalent resistance of an M×N resistor network is important, but difficult. In this paper, we present a standard and convenient approach to calculate the equivalent resistance of an M×N cobweb resistor network by applying multiple external current sources based on the nodal analysis in circuit theory and the recursion-transform (R-T) method. The test current source acts on different nodes in radial direction to obtain an analytical expression for the equivalent resistance between nodes of an M×N cobweb resistor network in radial direction. In our scheme, recalculations are not required to obtain the equivalent resistance between different radial nodes. We also discuss the influence of polygon sides of cobweb network and the ratio between two unit resistances on the equivalent resistance. The results show that, when the number of similar polygons M is given, with the increasing of the polygon sides and the ratio between two unit resistance, the equivalent resistances between two arbitrary radial nodes tend to a constant.

In this work, we derive the Langevin equation (LE) of a classical spin interacting with a heat bath through momentum variables, starting from the fully dynamical Hamiltonian description. The derived LE with anomalous dissipation is analyzed in detail. The obtained LE is non-Markovian with multiplicative noise terms. The concomitant dissipative terms obey the fluctuation–dissipation theorem. The Markovian limit correctly produces the Kubo and Hashitsume equation. The perturbative treatment of our equations produces the Landau–Lifshitz equation and the Seshadri–Lindenberg equation. Then we derive the Fokker–Planck equation corresponding to LE and the concept of equilibrium probability distribution is analyzed.

A quantum router can guide information from one quantum channel to another; thus, it has an increasingly important role in complex quantum networks. Here, we verify that the quantum router proposed by [L. Zhou et al., Phys. Rev. Lett 111, 103604 (2013)] achieves quantum-state high fidelity. When the transition strengths match $g_a=g_b$, the fidelity of the atom decreases from the maximum value after a period of time and then rises to a maximum value of 1; if the transition strengths do not match, the fidelity will not be able to reach 1.

We study the evolution of unstable front in reaction–diffusion systems analytically and derive the evolution equation for the fronts of a bistable system in the presence of advection. As an issue, we investigate the stability of planar fronts and explicitly show that the coupling to advection on the basis of the model of active fluids’ or, alternatively, on the model of an interfacial reaction can lead to an instability of the front, eventually leading to a fractalization of the chemical fronts.

The crystal structure and dielectric properties of TiO₂-modified Ca[(Li${}_{1/3}$Nb${}_{2/3}$)${}_{0.8}$Sn${}_{0.2}$]O${}_{3-\delta }$ microwave ceramics are investigated in the present paper. The crystal structure is probed by XRD patterns and their Rietveld refinement, results show that a single perovskite phase is formed in TiO₂-modified Ca[(Li${}_{1/3}$Nb${}_{2/3}$)${}_{0.8}$Sn${}_{0.2}$]O${}_{3-\delta }$ ceramics with the crystal structure belonging to the orthorhombic Pbnm 62 space group. Raman spectra results indicate that the $B$-site order–disorder structure transition is a key point to the dielectric loss of TiO₂-modified Ca[(Li${}_{1/3}$Nb${}_{2/3}$)${}_{0.8}$Sn${}_{0.2}$]O${}_{3-\delta }$ ceramics at microwave frequencies. After properly modified by TiO₂, the large negative temperature coefficient of Ca[(Li${}_{1/3}$Nb${}_{2/3}$)${}_{0.8}$Sn${}_{0.2}$]O${}_{3-\delta }$ ceramic can be compensated and the optimal microwave dielectric properties can reach ${𝜀}_r$ = 25.66, $Q_f$ = 18,894 GHz and TCF = −6.3 ppm/${}^{\circ }$C when sintered at 1170${}^{\circ }$C for 2.5 h, which manifests itself for potential use in microwave dielectric devices for modern wireless communication.

Zinc-based nanostructured nickel (Ni) free metal oxide electrode material Zn${}_{0.60}$/Cu${}_{0.20}$Mn${}_{0.20}$ oxide (CMZO) was synthesized by solid state reaction and investigated for low temperature solid oxide fuel cell (LTSOFC) applications. The crystal structure and surface morphology of the synthesized electrode material were examined by XRD and SEM techniques respectively. The particle size of ZnO phase estimated by Scherer’s equation was 31.50 nm. The maximum electrical conductivity was found to be 12.567 S/cm and 5.846 S/cm in hydrogen and air atmosphere, respectively at 600${}^{\circ }$C. The activation energy of the CMZO material was also calculated from the DC conductivity data using Arrhenius plots and it was found to be 0.060 and 0.075 eV in hydrogen and air atmosphere, respectively. The CMZO electrode-based fuel cell was tested using carbonated samarium doped ceria composite (NSDC) electrolyte. The three layers 13 mm in diameter and 1 mm thickness of the symmetric fuel cell were fabricated by dry pressing. The maximum power density of 728.86 mW/cm² was measured at 550${}^{\circ }$C.

Lead-free sodium niobate (NaNbO₃, NN) and potassium niobate (KNbO₃, KN) nanopowders were successfully synthesized by a simple and green synthesis process in gelatin media. Gelatin, which is a biopolymer, was used as stabilizer. In order to determine the lowest calcination temperature needed to obtain pure NN and KN nanopowders, the produced gels were analyzed by thermogravometric analyzer (TGA). The produced gels were calcined at 500${}^{\circ }$C and 600${}^{\circ }$C. The structural and optical properties of the prepared powders were examined using X-ray diffraction (XRD) technique, transmission electron microscopy (TEM), and UV–Vis spectroscopy. The XRD results revealed that pure phase NN and KN nanopowders were formed at low temperature calcination of 500${}^{\circ }$C and 600${}^{\circ }$C, respectively. The Scherrer formula and size-strain plot (SSP) method were employed to estimate crystallite size and lattice strain of the samples. The TEM images show that the NN and KN samples calcined at 600${}^{\circ }$C have cubic shape with an average particle size of 60.95 and 39.29 nm, respectively. The optical bandgap energy of the samples was calculated using UV–Vis diffused reflectance spectra of the samples and Kubelka–Munck relation.

We characterized the ultrafast properties of LT-GaAs doped with silicon $\delta$-layers and introduced delta-doping ($\delta$-doping) as efficient method for enhancing the properties of GaAs-based structures which can be useful for terahertz (THz) antenna, ultrafast switches and other high frequency applications. Low temperature grown GaAs (LT-GaAs) became one of the most promising materials for ultrafast optical and THz devices due to its short carrier lifetime and high carrier mobility. Low temperature growth leads to a large number of point defects and an excess of arsenic. Annealing of LT-GaAs creates high resistivity through the formation of As-clusters, which appear due to the excess of arsenic. High resistivity is very important for THz antennas so that voltage can be applied without the risk of breakdown. With $\delta$-Si doping, control of As-clusters is possible, since after annealing, clusters align in the plane where the $\delta$-doping occurs. In this paper, we compare the properties of LT-GaAs-based planar structures with and without $\delta$-Si doping and subsequent annealing. We used pump-probe transient reflectivity as a probe for ultrafast carrier dynamics in LT-GaAs. The results of the experiment were interpreted using the Ortiz model and show that the $\delta$-Si doping increases deep donor and acceptor concentrations and decreases the photoinduced carrier lifetime as compared with LT-GaAs with same growth and annealing temperatures, but without doping.

Graphene has vast promising applications in nanoelectronics and spintronics because of its unique magnetic and electronic properties. Making use of an ab initio spin-polarized density functional theory, implemented by the method of the Heyd–Scuseria–Ernzerhof 06 (HSE06) hybrid functional, the properties of various defect dopants in a supercell of a semi-metal monolayer graphene were investigated. We found from our calculation that introducing one defect dopant in a supercell would break the spin sublattice symmetry, and will induce a magnetic state at some appropriate doping concentrations. This paper systematically analyzes the magnetic effects of three types of defects on graphene, that is, vacancy, substitutional dopant and adatoms. Different types of defects will induce various new properties in graphene. The energies and electronic properties of these three types of defects were also calculated.

In this study, electrical parameters of the Al/Bi₄Ti₃O${}_{12}$/p-Si metal-ferroelectric-semiconductor (MFS) structure and their temperature dependence were investigated using current–voltage (I–V) data measured between 120 K and 300 K. Semi-logarithmic I–V plots of the structure revealed that fabricated structure presents two-diode behavior that leads to two sets of ideality factor, reverse saturation current and zero-bias barrier height (BH) values. Obtained results of these parameters suggest that current conduction mechanism (CCM) deviates strongly from thermionic emission theory particularly at low temperatures. High values of interface states and nkT/q−kT/q plot supported the idea of deviation from thermionic emission. In addition, $ln$(I)−$ln$(V) plots suggested that CCM varies from one bias region to another and depends on temperature as well. Series resistance values were calculated using Ohm’s law and Cheungs’ functions, and they decreased drastically with increasing temperature.

In this paper, we outline a scheme for the entanglement swapping procedure based on cavity quantum electrodynamics using the Jaynes–Cummings model consisting of the coherent and photon-added coherent states. In particular, utilizing the photon-added coherent states ($|$$\alpha ,m〉\simeq {â}^{†m}$$|$$\alpha 〉$, where $|\alpha 〉$ is the Glauber coherent state) in the scheme, enables us to investigate the effect of $m$, i.e., the number of excitations corresponding to the photon-added coherent field on the entanglement swapping process. In the scheme, two two-level atoms $A_1$ and $A_2$ are initially entangled together, and distinctly two exploited cavity fields $F_1$ and $F_2$ are prepared in an entangled state (a combination of coherent and photon-added coherent states). Interacting the atom $A_2$ with field $F_1$ (via the Jaynes–Cummings model) and then making detection on them, transfers the entanglement from the two atoms $A_1$, $A_2$ and the two fields $F_1$, $F_2$ to the atom-field “$A_1$-$F_2$”, i.e., entanglement swapping occurs. In the continuation, we pay our attention to the evaluation of the fidelity of the swapped entangled state relative to a suitable maximally entangled state, success probability of the performed detections and linear entropy as the degree of entanglement of the swapped entangled state. It is demonstrated that, an increase in the number of excitations, $m$, leads to the increment of fidelity as well as the amount of entanglement. According to our numerical results, the maximum values of fidelity (linear entropy) 0.98 (0.46) is obtained for $m=9$, however, the maximum value of success probability does not significantly change by increasing $m$.

We present a theoretical method based on Green’s function technique and tight-binding approach as well as harmonic approximation in order to calculate the coherent electronic conductance of an extended poly(p-phenylene) oligomer in the presence of thermal atomic vibrations. We study two proposed mass-spring models for atomic vibrations: one, including rigid benzene rings connected to each other by vibrating bonds; and in another, the bonds along the oligomer vibrate even in the benzene rings. The electron–phonon (e–ph) interaction influences the electron hopping energies linearly with respect to atomic displacements. The model shows that the conductance spectra exhibit some new energy gaps in the presence of e–ph interaction even at zero temperature. The conductance is more affected by e–ph interaction when the atomic vibrations are supposed to be present in the benzene rings. At the edges of the band energy and central gap, the phonon-assisted phenomena can be observed. Generally, the increasing e–ph interaction strength as well as temperature destroys the electronic conductance especially in the resonance region.