Modern Physics Letters B

A concise and somewhat personal review of the problem of superfluidity and quantum criticality in regular and disordered interacting Bose systems is given, concentrating on general features and important symmetries that are exhibited in different parts of the phase diagram, and that govern the different possible types of critical behavior. A number of exact results for various insulating phase boundaries, which may be used to constrain the results of numerical simulations, can be derived using large rare region type arguments. The nature of the insulator-superfluid transition is explored through general scaling arguments, exact model calculations in one dimension, numerical results in two dimensions, and approximate renormalization group results in higher dimensions. Experiments on ⁴He adsorbed in porous Vycor glass, on thin film superconductors, and magnetically trapped atomic vapors in a periodic optical potential are used to illustrate many of the concepts.

The effect of channel width on the density structure of confined fluid in the nano-/micro-channels is examined by equilibrium molecular dynamics (EMD) simulation. It was found that the density oscillation occurs near the wall in both cases of the macroscale or nanoscale confined flow. There exists a threshold channel width L_threshold, when channel width H<L_threshold, density oscillates throughout the channel. When H>L_threshold, L_threshold is constant and about 5–6 molecular diameter long, and the density becomes uniform beyond this threshold layer. A newly defined ch number may serve to be the parameter to compare similarity in the micro-/nano-scale channel flow. Moreover, the effect of the density oscillation on fluid mass flux rate is examined quantitatively. The result shows that the effect should be considered when the channel width is below 5 molecular diameter.

This paper presents a reconsideration of the levitation drift of YBaCuO superconductor induced by the vibration of a permanent magnet. On the descending curve, the drift occurs with decreasing levitation force, and on the departing process, the drift shows an increase of the levitation force except that the gap between the superconductor and magnet is small. A qualitative interpretation reveals the essence of the drift using the Preisach model.

Based on the coherent quantum transport theory, the spin polarization and tunneling magnetoresistance for polarized electrons through ferromagnetic/semiconductor/ferromagnetic (FM/SM/FM) heterostructure are studied theoretically within the Landauer framework of ballistic transport. The significant quantum size, quantum coherent, angle between the magnetic moments of the left and right ferromagnets, and Rashba spin-orbit interaction are considered simultaneously. The results indicate that the spin polarization and tunneling magnetoresistance are periodic functions of the semiconductor channel length, quasiperiodic functions of the Rashba spin-orbit coupling strength, and depend on the relative orientation of the two magnetizations in the left and right ferromagnets. A moderate angle, semiconductor channel length, and Rashba spin-orbit coupling strength allow a giant spin polarization or tunneling magnetoresistance. The results may be of relevance for the implementation of quasi-one-dimensional spin-transistor devices.

The transient properties of a bistable system with time-delayed feedback and non-Gaussian noise are investigated. The explicit expressions of the mean first-passage time (MFPT) are obtained. The numerical computations show that the MFPT of the system is affected by the delay time τ, the non-extensive index q and the color noise correlation time τ₀. That is, q can induce the MFPT from a complex behavior to a simple monotonous behavior with τ increasing (i.e. from two extrema to no extremum). But with the q increasing, the MFPT has a extremum, which is more large as τ increases.

Two types of white wines with different places of provenience, and a few types of commercial and natural juices were chosen for preliminary studies of their antioxidant characteristics by using Electron Paramagnetic Resonance (EPR) spectroscopy. Antioxidant capacity of these samples was assessed using stable free radicals such as nitroxide radical Tempol (2,2,6,6-tetramethyl-4-hydroxypiperidine-oxyl), as a paramagnetic agent. The inhibition by antioxidants of the absorbance of the paramagnetic species was found to decrease in time with different rates, and was correlated to the antioxidant activity of the studied samples. The obtained results permit us to make a brief evaluation of the main antioxidative characteristics of the studied wines and juices samples.

Samples of YBa₂Cu₃O_7-δ superconducting ceramic were prepared and characterized by resistivity measurements using the four probe method and structural analysis using X-ray diffraction (XRD). XRD-patterns show the presence of orthorhombic Y-123 phase with a small fraction of secondary phase, YBa₂Cu₃O₅. Samples were irradiated with gamma (γ) rays using Co⁶⁰ source with five successive doses of 2.5 Mrad. A monotonic increase in the T_c0 value was observed for radiation dosage up to 10 Mrad. When exposed to even higher γ-doses, the T_c0 value leveled off at a saturation value or decreased. XRD-analysis shows slightly changed values of the lattice constants and a mild shift of diffraction peaks towards a lower 2θ value. These observations indicate structural changes in YBa₂Cu₃O_7-δ induced upon gamma irradiation. The present work describes our experimental findings and attempts to offer a theoretical explanation for the effects observed.

Fourier and Bessel function solutions of two mixed derivative equations are investigated. For the appropriate sign of the material constants in the derivation of the mixed derivative equation, we obtain both Fourier and Bessel function solutions that tend to the corresponding solutions of the phenomenological diffusion equation. For the opposite sign of the material constants, the solutions diverge.