Multiple current states of two phase-coupled superconducting rings

The states of two phase-coupled superconducting rings have been investigated. Multiple current states have been revealed in the dependence of the critical current on the magnetic field. The performed calculations of the critical currents and energy states in a magnetic field have made it possible to interpret the experiment as the measurement of energy states into which the system comes with different probabilities because of the equilibrium and nonequilibrium noises upon the transition from the resistive state to the superconducting state.     

Primitive Illumination Systems for Families of Convex Bodies in the Plane

Let F= {C₁,C₂,...,C} be a family of ndisjoint convex bodies in the plane. We say that a set Vof exterior light sources illuminates F, if for every boundary point of any member of Fthere is a point in Vsuch that is visible from ,i.e. the open line segment joining and is disjoint from F. An illumination system Vis called primitive if no proper subset of Villuminates F. Let p_max(F) denote the maximum number of points forming a primitive illumination system for F, and letp_max(n) denote the minimum of F) taken over all families Fconsisting of ndisjoint convex bodies in the plane. The aim of this paper is to investigate the quantities p_max(F) and p_max(n).     

Attraction-repulsion transition between abrikosov vortices and Josephson vortices in the strongly layered superconductor Bi2Sr2CaCu2O8

A change in the effect of a frozen magnetic field parallel to the c-axis on rf power absorption, which is associated with the motion of Josephson vortices, is observed in the layered superconductor Bi₂Sr₂CaCu₂O₈ at a low temperature (～15 K). The effect is interpreted as a change in the interaction between an Abrikosov vortex and a Josephson vortex from attraction (at high temperatures) to repulsion (at low temperatures). It is found that the dynamics of the magnetic flux parallel to the ab plane of the single crystal becomes irreversible upon a transition of the superconductor to the layered state. Possible reasons behind the observed effect are considered, one of them being a manifestation of the second superconducting transition in the elementary-excitation spectrum of a d-type superconductor near the core of Abrikosov vortices.     

Differential pharmacokinetics and the brain distribution of morphine and ephedrine constitutional isomers in rats after oral administration with Keke capsule using rapid‐resolution LC–MS/MS

Opioid and ephedra alkaloids known as the active ingredients for Keke capsule, which is used to treat coughs and bronchial asthma, could have potential adverse effects on the central nervous system. Therefore, an efficient, sensitive rapid‐resolution LC–MS/MS method for the simultaneous determination of morphine, ephedrine, and pseudoephedrine in rat plasma and brain tissue homogenate has been developed. The method was validated in the plasma and brain tissue samples, showed good linearity over a wide concentration range (r² > 0.99). The intra‐ and interday assay variability was less than 15% for all analytes, and the accuracy was between ?8.8 and 5.7%. The study provided the pharmacokinetics profiles and the brain regional distribution of the three active alkaloids after oral administration of Keke capsule. The results also indicated that significant difference in pharmacokinetics parameters of the epimers was observed between ephedrine and pseudoephedrine.     

Dependence of the magnitude and direction of the persistent current on the magnetic flux in superconducting rings

The obtained periodic magnetic-field dependences I _c+(Φ/Φ₀) and I _c?(Φ/Φ₀) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I _c?(Φ/Φ₀) = I _c+(Φ/Φ₀ + Δ?) of the critical current measured in opposite directions. This shift means that the position of I _c+(Φ/Φ₀) and I _c?(Φ/Φ₀) minima does not correspond to n + 0.5 magnetic flux Φ quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I _{c, an}(Φ/Φ₀) = I _c+(Φ/Φ₀) ? I _c?(Φ/Φ₀) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature.     

Possibility of persistent voltage observation in a system of asymmetric superconducting rings

The possibility of observing persistent voltage in superconducting rings of different arm widths is experimentally investigated. It was previously found that switching of the arms between superconducting and normal states by an AC current induces DC voltage oscillation in the magnetic field with a period corresponding to the flux quantum inside the ring. We used systems with a large number of asymmetric rings connected in series to investigate the possibility of observing this quantum phenomenon near the superconducting transition, where thermal fluctuations lead to switching of ring segments without an external influence and the persistent current is much smaller than in the superconducting state.     

Critical behavior of electron spin resonance in La0.8Sr0.2MnO3 — a material with colossal magnetoresistance

High-frequency absorption in the colossal magnetoresistance material La_0.8Sr_0.2MnO₃ is investigated near the critical temperature in a magnetic field. The temperature dependences of the width, position, and intensity of the ESR line are studied in the near-critical region. Pis’fma Zh. éksp. Teor. Fiz. 67, No. 12, 1000–1004 (25 June 1998)     

Sensitivity Enhancement in Uranium Determination by UV-Visible Spectroscopy Using Ion Imprinted Polymer

There is need to determination of uranium concentration at ppb level in environmental matrices. Due to low sensitivity of FAAS, UV-Visible Spectroscopy is generally used as measurement technique. In this study, ion-imprinted polymers (IIP) were prepared for uranyl ion (imprint ion) by formation of ternary (salicylaldoxime and 4-vinylpyridine) complex in 2-methoxy ethanol (porogen) following copolymerization with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking monomer using 2,2-azobisisobutyronitrile as initiator. The synthesized polymers were characterized by FT-IR and TGA analysis. Arsenazo Ⅲ in 3 M HClO₄ was used as complexing agent in the measurement step. The optimal pH for preconcentration was found to be between 3.5～6.5 values. The developed method was applied to uranium (Ⅵ) determination in natural water samples.