Current-voltage characteristics of NdFeAsO0.85F0.15 and NdFeAsO0.85 superconductors

The vortex phase diagrams of NdFeAsO0.85F0.15 and NdFeAsO0.85 superconductors are determined from the analysis of resistivity and current-voltage (I-V) measurements in magnetic fields up to 9 T. A clear vortex glass to liquid transition is identified only in the oxygen deficient NdFeAsO0.85, in which I-V curves can be well scaled onto liquid and glass branches consistent with the vortex glass theory. With increasing magnetic field, the activation energy U0, deduced from the Arrhenius plots of resistivity based on the thermally activated flux-flow model (TAFF), decays more quickly for NdFeAsO0.85F0.15 than for NdFeAsO0.85. Moreover, the irreversibility field Hirr of NdFeAsO0.85 increases more rapidly than that of NdFeAsO0.85F0.15 with decreasing temperature. These observations evidence the strong vortex pinning effects, presumably caused by the enhanced defects and disorders in the oxygen deficient NdFeAsO0.85. It is inferred that the enhanced defects and disorder can be also responsible for the vortex glass to liquid transition in the NdFeAsO0.85.Comment: 19 pages, 5 figure

Quantum electric-dipole liquid on a triangular lattice

Geometric frustrations and quantum mechanical fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets that represents an exotic phase of matter and is attracting enormous interests. Geometric frustrations and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogs to quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled small electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19, in which small electric dipoles originated from the off-center displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional triangular lattice, represents a promising candidate to generate the anticipated electric-dipole liquid. We present a series of experimental evidences, including dielectric permittivity, heat capacity, and thermal conductivity measured down to 66 mK, to reveal the existence of a nontrivial ground state in BaFe12O19, characterized by itinerant low-energy excitations with a small gap, to which we interpret as an exotic liquid-like quantum phase. The quantum electric-dipole liquids in frustrated dielectrics open up a fresh playground for fundamental physics and may find applications in quantum information and computation as well.Comment: 13 pages, 6 figure

Isolation and open reading frame 5 gene analysis of porcine reproductive and respiratory syndrome virus in Yunnan Province, China

Two porcine reproductive and respiratory syndrome virus (PRRSV), respectively named YN-1 and YN-2 strains, were isolated by inoculation into Marc-145 cell. The two isolated strains induce Marc-145 cell stack together, pull net, form plaque and other typical lesions after 4 blind passages. With extracted viral RNA of fourth generation, reverse transcriptase (RT)-PCR based on open reading frame 5 (ORF5) gene showed that there was porcine reproductive and respiratory syndrome virus in Marc-145 cell of fourth generation. TCID50 of isolate measured by Reed-Muench method was 10-3.6/0.1 ml. Genetic evolution of ORF5 indicated that the two isolated strains were in a small branch with high identity of 99.5%. They were in a branch with Shandong strain JN-HS, Hennan-1 and Vietnam 347-T-KSA strain with identity of 99.2 to 99.8%. The two isolated strains were in a different branch with Ch-1a and VR-2332 strains having identity of 94.4 to 94.5%.Key words: Porcine reproductive and respiratory syndrome virus (PRRSV), isolation, ORF5 gene, genetic evolution