International Journal of Modern Physics B

We consider a large ensemble of globally coupled subthreshold Morris–Lecar neurons. We numerically investigate collective coherence of noise-induced spikings by varying the coupling strength J. As J passes a lower threshold, a transition to collective spiking coherence, which is described in terms of an order parameter, occurs because the coupling stimulates coherence between noise-induced spikings. However, when passing a higher threshold, the coupling induces oscillator death (i.e., quenching of noise-induced spikings) because each neuron is attracted to a noisy equilibrium state. Through competition of these two different roles of coupling, coupling-induced spiking coherence is found to occur in a large range of intermediate coupling strength. The degree of spiking coherence is well-characterized in terms of a coherence measure reflecting the degree of "resemblance" of the global potential to the local potential.

Nitrogen incorporated hydrogenated amorphous carbon (a-C:N:H) thin films have been deposited by microwave surface-wave plasma chemical vapor deposition on silicon and quartz substrates, using helium, methane and nitrogen (N₂) as plasma source. The deposited a-C:N:H films were characterized by their optical, structural and electrical properties through UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current-voltage characteristics. The optical band gap decreased gently from 3.0 eV to 2.5 eV with increasing N₂ concentration in the films. The a-C:N:H film shows significantly higher electrical conductivity compared to that of N₂-free a-C:H film.

The stationary phase method is often employed for computing tunneling phase times of analytically-continuous gaussian or infinite-bandwidth step pulses which collide with a potential barrier. The indiscriminate utilization of this method without considering the barrier boundary effects leads to some misconceptions in the interpretation of the phase times. After re-examining the above barrier diffusion problem where we notice the wave packet collision necessarily leads to the possibility of multiple reflected and transmitted wave packets, we study the phase times for tunneling/reflecting particles in a framework where an idea of multiple wave packet decomposition is recovered. To partially overcome the analytical incongruities which rise up when tunneling phase time expressions are obtained, we present a theoretical exercise involving a symmetrical collision between two identical wave packets and a one-dimensional squared potential barrier, where the scattered wave packets can be recomposed by summing the amplitudes of simultaneously reflected and transmitted waves.

In the present paper, by applying the reflection positivity method due to Dyson, Lieb, and Simon, we rigorously establish the sufficient condition for existence of the Néel long-range order (NLRO) in two-dimensional spin-1/2 XXZ. Our result shows that if the anisotropic coupling Δ satisfies 0 ≤ Δ ≤ 0.30 or Δ ≥ 1.52, the existence of the NLRO along easy axis is proved.

We investigate the effect of nonuniform transmission on the critical threshold of susceptible–infected–recovered–susceptible (SIRS) epidemic model on scale-free networks. Based on the mean-field theory, it is observed that the epidemic threshold is not only correlated with the topology of underlying networks, but also with the disease transmission mechanism (e.g., nonuniform transmission). The current findings will significantly help us to further understand the real epidemics taking place on social and technological networks.

Dipole and cavity field transient spectra are investigated for a modified Jaynes-Cummings (JC) model due to the presence of a second harmonic generation (SHG) cavity field. For initially de-excited atom and field in a coherent state, detuning effects due to SHG affects the symmetry and splitting structure of both spectra.

A set of AlN thin films was prepared by reactive magnetron sputtering at room temperature. The effect of oxygen impurities on the structural and optical properties of AlN films is discussed. The structural and optical properties were characterized using X-ray diffraction (XRD) and spectroscopic ellipsometry, respectively. Depending on the deposition conditions, films can grow hexagonal (würzite, P6₃m3) or cubic (zinc-blende, Fm3m) in microstructure. From the optical measurements, the ellipsometric parameters (ψ, Δ) and the real refractive index as a function of energy were obtained. From the ellipsometric measurements, a model of Lorentz single-oscillator was employed to estimate the optical band gap, E_g. In the theoretical part, a calculation of density of states (DOS) and band structure was performed to be compared with the experimental results.

The critical behavior of the specific heat is studied in s-triazine (C₃N₃H₃). Using the experimental data for the C_P, the temperature dependence of the specific heat is analyzed according to a power-law formula and the values of the critical exponent for C_P are extracted in the vicinity of the transition temperature (T_C=198.07 K).

It is indicated that s-triazine undergoes a weakly first order (quasi-continuous) or second order phase transition.

Using the extended homogeneous balance method, we obtain a new type of multiple solitary wave solutions for the (1+1)-dimensional high-order Broer–Kaup equations and a new type of multiple solitary wave-like solutions for the (2+1)-dimensional high-order BK equations. The method used here is very concise and primary, and can be generalized to deal with other class of nonlinear equation.

We investigate the evolution of the atomic quantum entropy and the atom-field entanglement in a system of a Ξ-configuration three-level atom interacting with a single-mode field with additional forms of nonlinearities of both the field and the intensity-dependent atom-field coupling. With the derivation of the unitary operator within the frame of the dressed state and the exact results for the state of the system, we perform a careful investigation of the temporal evolution of the entropy. A factorization of the initial density operator is assumed, considering the field to be initially in a squeezed coherent or binomial state. The effects of the mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy are analyzed.

A new kind of synchronization in which some well-defined functions of dynamical variables tend to each other as time evolves is shown to take place in two distinct three-dimensional nonlinear systems. This new kind of functional synchronization is analyzed using the partial Lyapunov functions which help one to construct the functions of the nonlinear variables which synchronize. In the next phase we show how one can develop a set of keys to encode and decode a signal which is to be transmitted. Since the key construction is very much dependent on the chosen function, the whole system is highly secure.