Modern Physics Letters B

This research is focused on mathematical modeling of fluids with yield stress in the squeeze mode. The focus of the research is on magneto-rheological (MR) fluids but the results can be extended to any non-Newtonian fluid exhibiting a yielding behavior. There is no universally accepted mathematical model of squeeze flow of MR fluids to date because of the complexity of the flow and lack of theoretical and experimental studies. In this research, the squeeze flow problem of MR fluids is solved using perturbation techniques and squeeze force and flow field are determined. The model is verified and validated using experimental test data and it is shown that the model can be used as a design tool for design of MR devices that operate in the squeeze mode.

Using a first-principle band-structure method and a special quasirandom structure (SQS) approach, we present state-of-the-art HSE06 functional calculations for demonstrating the possibility of ternary Pb_xZn_1-xTe alloys to be bipolar-doping materials. The results show that the bowing parameters and the band gaps of these alloys sensitively depend on the composition x. Due to the full overlapping and delocalization, the coupling between Pb outermost p orbits and Zn 4s orbits become very strong, thus resulting in a significant downshift of conduction band edge with the increase of Pb concentration x. When the concentration x reaches 0.25, it is demonstrated that the Pb_0.25Zn_0.75Te alloy has a substantial decrease in the conduction band edge, while leaving the valence band edge almost unchanged compared to that of binary ZnTe, thus improving the possibility for ambipolar-doping. Meanwhile, the spectral response of this alloy (E_g = 1.38 eV) is very consistent with the solar spectrum. We expect that our results will be helpful for the applications of optoelectronic devices.

We study the Cole–Cole diagram for the case of a paraelectric particle for which the relaxation time is the same for every mode and the resonance frequency changes and there is an infinite number of such modes. We will calculate the Cole–Cole diagram for temperature a = 10 and damping g = 1 in a and g units (see below) from exact expression for the dynamic susceptibility. We have found that there is a smooth Cole–Cole diagram the curve of which starts from small frequencies 0.001 from the point near Y = 1.5 and X = 0 on the diagram down to the peak (in imaginary part) values of X near 1.6 and Y near 0.5 increasing frequency. Increasing further frequency to 20, the real and imaginary parts tend to zero value. Thus there exists a single maximum of the imaginary part of the susceptibility (for 1000 modes and for 5000 modes), and a single maximum and minimum for the real part of the susceptibility.

The state function entropy and its quantum thermodynamical implication for two typical dissipative systems with anomalous spectral densities are studied by investigating on their low-temperature quantum behavior. In all cases, it is found that the entropy decays quickly and vanishes as the temperature approaches zero. This reveals a good conformity with the third law of thermodynamics and provides another evidence for the validity of fundamental thermodynamical laws in the quantum dissipative region.

By using the field-theoretical techniques combining bosonization with renormalization group, we study a one-dimensional (1D) model of interacting electrons with on-site repulsion (U > 0), nearest-neighbor (nn) exchange (J) and correlated-hopping (t₂, t₃) interactions at weak coupling. In the case of a half-filled band, the two-body interaction t₂ does not influence phase diagram of the model, while the presence of three-body interaction t₃ makes the physics of the system highly non-trivial. By a Hartree–Fock decoupling, the effects of t₃ bring about hopping of pairs, V-like (nn Coulomb interaction) and isotropic exchange terms in the reduced model Hamiltonian. Interestingly, a negative t₃ provides a possibility for the occurrence of the triplet superconductivity in 1D system with purely repulsive interactions (U, J > 0). The ground state phase diagram including the insulating and superconducting phases is discussed analytically.

Upon considering the three interactions namely, the electron–acoustic phonon, the electron–optical phonon and the Coulomb, the analytical solutions for the energy gap equation allows one to determine the electronic structure parameters to discuss the behavior of superconducting transition temperature (T_c) and isotope effect coefficient (α) for layered structure YNi₂ B₂C. T_c of 17 K is estimated for YNi₂B₂C with electron–acoustic phonon (λ_ac) = 0.31, electron–optical phonon (λ_op) = 0.1 and Coulomb screening parameter (μ*) = 0.126 indicating that the YNi₂B₂C superconductor is in the intermediate coupling regime. To correlate the T_c with various coupling strengths as λ_ac, λ_op and μ*, we present curves of T_c with them. The present approach also explains the conditions for the Boron and Carbon isotope effect. The negative pressure coefficient of T_c in this layered material is attributed to the contraction along c-axis under hydrostatic pressure. We suggest from these results that both the acoustic and optical phonons within the framework of a three-square well scheme consistently explains the effective electron–electron interaction leading to superconductivity in layered structure YNi₂B₂C.