492 research outputs found
Vortex Phase Diagram of weakly pinned YBaCuO for H c
Vortex phase diagram in a weakly pinned crystal of YBCO for H c
is reviewed in the light of a recent elucidation of the process of `inverse
melting' in a Bismuth cuprate system and the imaging of an interface between
the ordered and the disordered regions across the peak effect in 2H-NbSe.
In the given YBCO crystal, a clear distinction can be made between the second
magnetization peak (SMP) and the peak effect (PE) between 65 K and 75 K. The
field region between the peak fields of the SMP (H) and the onset
fields of the PE (H)is not only continuously connected to the Bragg
glass phase at lower fields but it is also sandwiched between the higher
temperature vortex liquid phase and the lower temperature vortex glass phase.
Thus, an ordered vortex state between H and H can get
transformed to the (disordered) vortex liquid state on heating as well as to
the (disordered) vortex glass state on cooling, a situation analogous to the
thermal melting and the inverse melting phenomenon seen in a Bismuth cuprate.Comment: Presented in IWCC-200
Double Giant Dipole Resonance in ^{208}Pb
Double-dipole excitations in ^{208}Pb are analyzed within a microscopic model
explicitly treating 2p2h-excitations. Collective states built from such
2p2h-excitations are shown to appear at about twice the energy of the isovector
giant dipole resonance, in agreement with the experimental findings. The
calculated cross section for Coulomb excitation at relativistic energies cannot
explain simultaneously the measured single-dipole and double-dipole cross
sections, however.Comment: 7 pages, Latex, 5 postscript figure
Dynamics vs electronic states of vortex core of high-T_c superconductors investigated by high-frequency impedance measurement
Dynamics of vortices reflects the electronic states of quasiparticles in the
core. To understand this, we investigated the following three issues. (1) We
investigated the complex surface impedance, Zs, of YBa2Cu3Oy as a function of
magnetic field, H. The total features were well expressed by the Coffey-Clem
model. From the data, we estimated the viscosity and pinning frequency, which
were found to be independent of frequency. In particular, the obtained
viscosity definitely shows that the core of vortex of YBa2Cu3Oy is moderately
clean. This result suggests that new physics will show up, for the physics of
quantum moderately clean vortex core is unknown at all. (2) An anomaly found in
the surface reactance at the first order transition (FOT) of vortex lattice was
investigated in Bi2Sr2CaCu2Oy with various doping levels. As a result, the
anomaly was found only in the samples exhibiting the FOT. On the other hand, we
did not observe the anomaly in YBa2Cu3Oy. These suggest that the anomaly is due
to the change in the electronic states of the vortices characteristic of
materials with very strong anisotropy. (3) We measured H dependence of both the
thermal conductivity \kappa(H) and Zs(H) in exactly the same pieces of crystal.
We could not find any anomaly in Zs(H) even at the onset of the plateau. This
result suggests that the origin of the plateau in \kappa(H) is not a drastic
phase transition but is rather gradual crossover.Comment: 6 pages, 5 figures, Proceedings of Plasma2000(Sendai), to be
published in Physica
Mechanism of spin-triplet superconductivity in Sr2RuO4
The unique Fermi surfaces and their nesting properties of Sr2RuO4 are
considered. The existence of unconventional superconductivity is shown
microscopically, for the first time, from the magnetic interactions (due to
nesting) and the phonon-mediated interactions. The odd-parity superconductivity
is favored in the and sheets of the Fermi surface, and the
various superconductivities are possible in the sheet. There are a
number of possible odd-parity gaps, which include the gaps with nodes, the
breaking of time-reversal symmetry and .Comment: 4 pages, 3 figure
Significance of Liver Size in Hepatic Surgery
The purpose of this study was to evaluate the significance of liver volumetry as a parameter for hepatic functional reserve in cirrhotic patients with hepatocellular carcinoma. Liver volume was calculated from preoperative computed tomograms of 44 cirrhotic patients who underwent elective hepatic resections for hepatocellular carcinoma
Effect of electron irradiation on vortex dynamics in YBa_2Cu_3O_{7-x} single crystals
We report on drastic change of vortex dynamics with increase of quenched
disorder: for rather weak disorder we found a single vortex creep regime, which
we attribute to a Bragg-glass phase, while for enhanced disorder we found an
increase of both the depinning current and activation energy with magnetic
field, which we attribute to entangled vortex phase. We also found that
introduction of additional defects always increases the depinning current, but
it increases activation energy only for elastic vortex creep, while it
decreases activation energy for plastic vortex creep.Comment: 4 pages, 3 figures, submited to Phys. Rev.
Disorder Effect on the Vortex Pinning by the Cooling Process Control in the Organic Superconductor -(BEDT-TTF)Cu[N(CN)]Br
We investigate the influence of disorders in terminal ethylene groups of
BEDT-TTF molecules (ethylene-disorders) on the vortex pinning of the organic
superconductor -(BEDT-TTF)Cu[N(CN)]Br. Magnetization
measurements are performed under different cooling-processes. The second peak
in the magnetization hysteresis curve is observed for all samples studied, and
the hysteresis width of the magnetization becomes narrower by cooling faster.
In contradiction to the simple pinning effect of disorder, this result shows
the suppression of the vortex pinning force by introducing more
ethylene-disorders. The ethylene-disorder domain model is proposed for
explaining the observed result. In the case of the system containing a moderate
number of the ethylene-disorders, the disordered molecules form a domain
structure and it works as an effective pinning site. On the contrary, an excess
number of the ethylene-disorders may weaken the effect of the domain structure,
which results in the less effective pinning force on the vortices.Comment: 6 pages, 6 figure
The difference in congenital cholesteatoma CT findings based on the type of mass
AbstractObjectiveA retrospective assessment of differences in congenital cholesteatoma CT findings with a focus on type of cholesteatoma mass.Materials and methodsThe medical records and CT images of 14 patients with congenital cholesteatomas in the middle ear who underwent surgery at our institution between January 2009 and July 2014 were reviewed. Cholesteatomas were classified as closed type, open type, or mixed type based on intraoperative findings. The CT findings including cholesteatoma size, location, and shape were retrospectively reviewed.ResultsEight patients had closed type cholesteatomas, four had mixed type, and two had open type. The mean size of all cholesteatomas was 5.1mm. None of the cholesteatoma types indicated a tendency towards a certain location. The round shape was observed more frequently in closed type cholesteatomas than in other types (closed: 5/8; mixed: 1/4; open: 0/2). Two large closed type cholseteatomas and two mixed type cholesteatomas exhibited a constricted shape. Both of the open type cholesteatomas displayed an irregular shape.ConclusionSmall closed type congenital cholesteatomas were typically observed as round shaped lesions, but large closed type cholesteatomas and other type cholesteatomas tended to display shapes other than round
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