Modern Physics Letters B

It is shown that Cooper pairs are a solution of the bipolaron problem for model Fröhlich Hamiltonian. The total energy of a pair for the initial Fröhlich Hamiltonian is found. Differences between the solutions for the model and initial two-particle problems are discussed.

With the aim of providing an analytical approach (not accurate numerical results), for the first time, the sensitivity to the partial pressure of oxygen of the shift in the energy band gap experienced by cadmium-oxide thin films is evaluated for the visible region by introducing a suitable parameter. The sensitivity to the above pressure of the spatial carrier density is determined and compared with the sensitivity relative to the band gap shift. The gradient of the CdO carrier concentration as a function of the partial pressure of oxygen appears in the expressions for the two above sensitivity functions but the goal of this paper is not computing numerically this gradient so only qualitative estimations are done. In relation to the above results, the kinetics relative to the formation of CdO thin films are investigated. In addition, the sensitivity to the pressure in question of the corresponding optical-absorption shift in the visible range is calculated.

We investigate the characteristics of resonant modes in the side-coupled rectangular-ring resonator (SRR). The results show we can manipulate the resonant wavelengths of TM_a mode and TM_s mode by adjusting the outer wall width (Lx1) or the inner wall width (Lx2) of the ring resonators, and the effects of coupling distance on the full-width at half-maximum (FWHM) of resonant spectra are discussed. In sensing application, the proposed structure can work as a highly sensitive plasmonic nanosensor with a sensitivity of 1000 nm/RIU and a figure of merit (FOM) of 67. The values are comparable to periodic structures and the structures based on Fano resonance.

In this paper, stainless steel was welded by active flux-aided laser welding method. The effects of single active flux (Cr₂O₃, SiO₂ and TiO₂) and composite active flux on laser welding were studied. In the welding process, laser plasma behavior was recorded by a high-speed imaging system. The results show that, with the addition of active flux, the absorption of laser energy and melting efficiency increase. In the laser power of 750 W, effects of active flux on weld depth to width ratio are given by the order: composite active flux $>$ SiO${}_2>$ Cr₂O${}_3>$ TiO₂. The effect of composite active flux is the most significant and it can increase the weld depth to width ratio to 85%. Active flux can restrict the laser plasma. With the addition of composite active flux, the projected area of laser plasma obtained obviously reduced, and it can be reduced by 41.39%. Active flux cannot obviously change the main components in weld zone, but can change the grains of austenite and ferrite.

A tunable power splitter based on metal-dielectric metal (MDM) waveguide coupled with rectangle cavity with Kerr nonlinear material is proposed. The power splitter properties are simulated by the finite-difference time-domain (FDTD) method [Y. H. Guo et al., Opt. Express 19 (2011) 13831–13838]. Simple theoretically analysis and numerically calculation demonstrate that the waveguide-rectangle cavity coupled system performs a tunable plasmonic power splitter. Additionally, the output power ratio can be efficiency tuned by varying the control light intensity. Results obtained by the coupled mode theory are consistent with those from the FDTD simulation. The plasmonic splitter may become a choice for the highly integrated optical circuits.

Stochastic resonance (SR) of a tristable system driven by dichotomous noise (DN) is investigated firstly by the mean signal-to-noise ratio gain (SNR-GM). Utilizing an efficiently numerical algorithm, we acquire the asymmetric DN accurately. Then the system responses and the SNR-GM as the signatures of the stochastic resonance are calculated by the fourth-order Runge–Kutta algorithm. It is founded that the change of system parameters $a$ and $c$ in a certain range can induce SR phenomenon. Moreover, with the increase of parameter $c$, the amplitude of SNR-GM increases and shows the trend of moving to the left. For the different state values of the symmetric DN, the SNR-GM will increase with the increase of state value $a_1$ and $b_1$ but only a highest peak and the interval of SR shift to the left. However, with the increase of forcing frequency, the SNR-GM decreases and the interval of SR moves to right. In addition to, the highest peak of SNR-GM will decrease with the increase of periodic signal amplitude. These results provide a reliable basis for how to realize the parameter selection of stochastic resonance in tristable system driven by DN.

In this work, we apply entropic sampling simulations to a three-state model which has exact solutions in the microcanonical and grand-canonical ensembles. We consider N chains placed on an unidimensional lattice, such that each site may assume one of the three states: empty (state 1), with a single molecule energetically null (state 2), and with a single molecule with energy $𝜀$ (state 3). Each molecule, which we will treat here as dimers, consists of two monomers connected one to each other by a rod. The thermodynamic properties such as internal energy, densities of dimers and specific heat were obtained as functions of temperature, where the analytic results in the microcanonical and grand-canonical ensembles were successfully confirmed by the entropic sampling simulations.

New research with modern technologies has always grabbed substantial attention. Conservation of raw materials like natural fibers has helped composite world to explore eco-friendly components. The aim of this paper is to study the potential of jute fiber-reinforced ceramic polymers. Alkali-treated jute fiber has been incorporated in a polypropylene ceramic matrix at different volume fractions. The morphological, thermal and optical studies of jute-reinforced ceramic Pb₂Sr₂CaCu₂O₉ (PbSrCaCuO) are studied. Morphological results evidently demonstrate that when the polypropylene ceramic matrix is reinforced with jute fiber, interfacial interaction between the varying proportions of the jute fiber and ceramic composite takes place. TGA and DSC results confirm the enhancement in the thermal stability of ceramic composites reinforced with jute fiber. The UV analysis of the composite gives a good quality measure on the optical properties of the new composite prepared.

New model of the pinning potential barrier in multilayered HTc superconductors is presented, based on geometrical approach to the capturing interaction of pancake-type vortices with nano-sized defects. Using the above model the transport current flow phenomena in these materials, especially the current–voltage characteristics and critical current density, have been considered. Details of theoretical analysis are given, including the derivation of basic mathematical equations describing the potential barrier as a function of transport current intensity and the initial position of captured pancake vortex. Computer simulation has been performed of the influence of transport current amplitude on the potential barrier height for various sizes of pinning centers and initial pancake vortex position as well as the influence of fast neutrons irradiation creating nano-sized defects on critical current of HTc layered superconductor.

We propose AND and OR logic gates based on a phononic crystal (PNC) ring resonator cavity. The proposed devices consist of ring resonator cavities coupled to PNC line defect waveguides. The logic gate performance has been analyzed and investigated using finite element methods. The design specifies a logical 0 as a transmission rate of 0.3 or less and a logical 1 as a transmission rate of 0.6 or more. The results show that such a design has stable transmission peaks, meeting the requirements of acoustic logic gates. The design has the potential to be a key component in future phononic integrated circuits.