High-frequency absorption of the dynamic mixed state in the surface superconductivity region

We analyze the absorption of a high-frequency electromagnetic field in the type II superconductor Pb_0.8In_0.2 in magnetic fields H _c2 < H < H _c3. The absorption component proportional to the rate of variation of the external magnetic field is detected. We assume that this absorption component is associated with the dynamic mixed state of the superconducting shell containing 2D magnetic flux vortices (Kulik vortices). The motion of these vortices under the action of the critical current ensures the required difference between the external and internal magnetic inductions of the superconducting shell upon a change in the external magnetic field. This model correctly describes the observed behavior of absorption of rf electromagnetic radiation.     

Quantum oscillations of the critical current of asymmetric superconducting rings

The current-voltage characteristics and the magnetic field dependences of the critical current have been measured for symmetric and asymmetric superconducting rings and systems of such rings. The dependences obtained explain the periodic change in the rectified voltage observed on asymmetric rings as a result of a periodic change in the asymmetry of current-voltage characteristics.     

Nanostructure of Dispersed and Compact Nonstoichiometric Vanadium Carbide

Structure and properties of dispersed and compact nanocrystalline vanadium carbide VC0.875 were studied. Dispersed vanadium nanocarbide was prepared by prolonged aging of a coarse-grained VC0.875 powder. It has a unique nanostructure: nanocrystallites of dispersed vanadium carbide have a shape of bent lobes up to 600 nm in diameter and 15-20 nm thick. Annealing and quenching of compact samples of coarsegrained VC0.875 carbide result in the formation of a nanodomain structure. The nanostructured carbide VC0.875 corresponds in composition to the higher boundary of a homogeneity area of a cubic phase and mainly contains ordered V8C7 phase, which belongs to the P4₃32 space group. Cold pressing and subsequent vacuum sintering of vanadium carbide nanopowder at 2000 K gave sintered samples approaching diamond in microhardness.     

Explosive transition in amorphous microwire

An amorphous microwire in a glass shell offers a quick thermal response and can be rapidly heated to the crystallization point. When heated by a current pulse with a small amplitude and duration, the wire passes from the amorphous to microcrystalline state. The crystallization of the amorphous state may represent a slow or explosive process depending on the parameters of the pulse. In the latter case, the emission of electromagnetic waves (flash of light) and a sharp rise in the resistance are observed. The rate of propagation of the crystallization front in our experiments has been found to be about 1 m/s.     

Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta.     

Dynamics of the magnetic flux component normal to the layers of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8</Subscript> in a tilted field

High-frequency losses in the strongly anisotropic layered superconductor Bi₂Sr₂CaCu₂O₈ are measured at 600 MHz under a magnetic field rocking about the ab plane. Anomalies in losses and hysteretic phenomena are found while performing periodic rocking, i.e., cycling the magnetic field component normal to the sample surface. Based on these observations, conclusions are drawn about the nature of magnetic-flux penetration into the superconductor. It is found that, in the range between 60 K and T _c , the dynamics of magnetic-flux vortex lines normal to the ab plane in the presence of a constant magnetic field applied parallel to this plane is governed by the critical penetration field H _c ^⊥* and the surface barrier in the presence of thermally activated vortex motion (giant flux creep). The dependences of H _c1 ^⊥* and the characteristic field of the surface barrier on the magnitude of the parallel magnetic field are measured.     

Comparative pharmacokinetics and tissue distribution of schisandrin,deoxyschisandrin and schisandrin B in rats after combining acupuncture and herb medicine (schisandra chinensis)

Recently, combination therapy with acupuncture and medicine as a practical strategy to treat diseases has gained increasing attention. The present study aimed to investigate whether acupuncture stimulation at ST.36 had a potential impact on the pharmacokinetics and tissue distribution of lignans. An HPLC‐ESI/MS analytical method was established and successfully applied to a comparative study of drug concentration in plasma and tissues of three lignans. The parameters area under the plasma concentration–time curve from time zero to the final measurable point and from time zero to infinity, and peak concentration were significantly increased, with a prolonged mean residence time and a corresponding decrease in clearance in comparision with the Schisandra‐alone group. Additionally, tissue concentrations of three lignans were improved in the group with acupuncture, especially in liver. The results indicated that acupuncture has a synergistic effect on the pharmacokinetics and tissue distribution of the three lignans, which could postpone their elimination, resulting in a longer blood circulating time in rat plasma and prolonged residence time in target tissues, leading to higher tissue concentration. The findings provide some scientific evidence for the mechanism of the combined use of acupuncture and herbal medicine. Furthermore, we suggest that acupuncture and its combination with herbal medicine should be investigated further as a possible adjuvant therapy in clinical treatment for liver injury. Copyright © 2014 John Wiley & Sons, Ltd.     

On the Shape and Dimensions of Three-Dimensional Cavities in Supercavitating Flows

The shape of long, trailing cavities behind three-dimensional headforms is discussed. The case of a flat elliptic wing is specifically treated. Three distinct shape regimes are found: quasi-planar, long-flat, spheroidal. These appear in successively higher speed ranges (lower cavitation numbers, ). It is argued that the cavities may be replaced by surrogates in the form of slender ellipsoids. The pressures on these are almost constant and correspond to a cavitation number equal to twice their longitudinal added mass coefficient, k₁. A heuristic theory based on kinetic energy fields is given, relating k₁ to the product of headform drag and cavity length. This theory correlates with an exact theory in the same form given by Garabedian for axi-symmetric cones and also with its extension to planar flows. Results are given here for the shape of the cavity behind an elliptic wing of any aspect ratio, given drag, and cavitation number. Specific formulae are given in the form, = f (C_D/AR), for the transition between the quasi-planar and long-flat regime, and the long-flat and spheroidal regime.     

Superconducting quantum interference device without Josephson junctions

A new type of a superconducting quantum interference device (SQUID) based on a single superconducting loop without Josephson junctions and with asymmetric contacts has been proposed. This SQUID offers advantages in simplicity of fabrication and a steeper dependence of measured quantities on the magnetic flux. To confirm the possibility of making this type of SQUID, the magnetic field dependence of the critical current in an aluminum ring with asymmetric contacts has been experimentally investigated.