2,432 research outputs found
Josephson Plasma Resonance in Solid and Glass Phases of BiSrCaCuO
Vortex matter phases and phase transitions are investigated by means of
Josephson plasma resonance in under-doped BiSrCaCuO
single crystals in a microwave frequency range between 19 and 70 GHz.
Accompanied by the vortex lattice melting transition, a jump of the interlayer
phase coherence extracted from the field dependence of the plasma frequency was
observed. In the solid phase, the interlayer coherence little depends on field
at a temperature region well below while it gradually decreases as field
increases toward the melting line up to just below . As a result, the
magnitude of the jump decreases with increasing temperature and is gradually
lost in the vicinity of . This indicates that the vortex lines formed in
the vortex solid phase are thermally meandering and the phase transition
becomes weak especially just below .Comment: 5pages and 4 figures. Submitted to Physica C (Proceedings of
Plasma2000, Sendai
Two Phase Collective Modes in Josephson Vortex Lattice in Intrinsic Josephson Junction BiSrCaCuO
Josephson plasma excitations in the high superconductor
BiSrCaCuO have been investigated in a wide microwave
frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied
parallel to the plane of the single crystal. In sharp contrast to the case
for magnetic fields parallel to the c axis or tilted from the plane, it
was found that there are two kinds of resonance modes, which are split in
energy and possess two distinctly different magnetic field dependences. One
always lies higher in energy than the other and has a shallow minimum at about
0.8 kOe, then increases linearly with magnetic field. On the other hand,
another mode begins to appear only in a magnetic field (from a few kOe and
higher) and has a weakly decreasing tendency with increasing magnetic field. By
comparing with a recent theoretical model the higher energy mode can naturally
be attributed to the Josephson plasma resonance mode propagating along the
primitive reciprocal lattice vector of the Josephson vortex lattice, whereas
the lower frequency mode is assigned to the novel phase collective mode of the
Josephson vortex lattice, which has never been observed before.Comment: 11 pages and 10 figure
The risk of rabies spread in Japan: a mathematical modeling assessment
Rabies was eliminated from Japan in 1957. In the 60 years since elimination, vaccination coverage has declined and dog ownership habits have changed. The purpose of this study was to assess the current risk of rabies spread in Japan. A spatially explicit transmission model was developed at the 1 km2 grid scale for Hokkaido and Ibaraki Prefectures. Parameters associated with dog movement and bite injuries were estimated using historical records from Japan, and were used with previously published epidemiological parameters. The final epidemic size, efficacy of rabies contingency plans and the influence of dog owner responses to incursions were assessed by the model. Average outbreak sizes for dog rabies were 3.1 and 4.7 dogs in Hokkaido and Ibaraki Prefectures, respectively. Average number of bite injury cases were 4.4 and 6.7 persons in Hokkaido and Ibaraki Prefectures, respectively. Discontinuation of mandatory vaccination increased outbreak sizes in these prefectures. Sensitivity analyses showed that higher chance of unintentional release of rabid dogs by their owners (from 0.5 to 0.9 probability) increased outbreak size twofolds. Our model outputs suggested that at present, incursions of rabies into Japan are very unlikely to cause large outbreaks. Critically, the reaction of dog owners to their dogs developing rabies considerably impacts the course of outbreaks. Contingency measures should therefore include sensitisation of dog owners
Superconducting Plasma Excitation at Microwave Frequencies in Parallel Magnetic Fields in
Josephson plasma resonance has been studied in a wide microwave frequency
range between 10 and 52 GHz in a magnetic field parallel to the -plane in
under-doped \BI. Above about 30 GHz two resonance modes were observed: one
(LT mode) appears at low temperatures and another (HT mode) at higher
temperatures, leaving a temperature gap between two regions. These two
resonance modes exhibit a sharp contrast each other both on temperture and
magnetic field dependences and show distinct characters different entirely from
the c-axis Josephson plasma resonance. From temperature and field scan
experiments at various frequencies it is suggested that the LT mode can be
attributed to the coupled Josephson plasma mode with Josephson vortices, while
the HT mode is a new plasma mode associated possibly with the periodic array of
Josephson vortices.Comment: submitted to Physica C (Prceedings of Plasma2000, Sendai
New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field
The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured
below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of
a parallel field, a new peak appears at finite frequency in the optical
conductivity at the expense of suppression of c-axis condensate weight. We
conclude that the dramatic change originates from different Josephson coupling
strengths between bilayers with and without Josephson vortices. We find that
the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under
parallel magnetic field; this indicates that the condensate weight at \omega =0
is distributed to the intra-bilayer mode as well as to the new optical
Josephson mode.Comment: 4 pages, 3 figure
Peak effect and dynamic melting of vortex matter in NbSe crystals
We present a mode locking (ML) phenomenon of vortex matter observed around
the peak effect regime of 2H-NbSe pure single crystals. The ML features
allow us not only to trace how the shear rigidity of driven vortices persists
on approaching the second critical field, but also to demonstrate a dynamic
melting transition of driven vortices at a given velocity. We observe the
velocity dependent melting signatures in the peak effect regime, which reveal a
crossover between the disorder-induced transition at small velocity and the
thermally induced transition at large velocity. This uncovers the relationship
between the peak effect and the thermal melting.Comment: To appear in Physical Review Lette
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