13,053 research outputs found
Charge dynamics in thermally and doping induced insulator-metal transitions of (Ti1-xVx)2O3
Charge dynamics of (Ti1-xVx)2O3 with x=0-0.06 has been investigated by
measurements of charge transport and optical conductivity spectra in a wide
temperature range of 2-600K with the focus on the thermally and doping induced
insulator-metal transitions (IMTs). The optical conductivity peaks for the
interband transitions in the 3d t2g manifold are observed in the both
insulating and metallic states, while their large variation (by ~0.4 eV) with
change of temperature and doping level scales with that of the Ti-Ti dimer bond
length, indicating the weakened singlet bond in the course of IMTs. The
thermally and V-doping induced IMTs are driven with the increase in carrier
density by band-crossing and hole-doping, respectively, in contrast to the
canonical IMT of correlated oxides accompanied by the whole collapse of the
Mott gap.Comment: 4 pages, 4 figure
Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei II. Prediction from our Sweeping Magnetic Twist Model for the Wiggled Parts of AGN Jets and Tails
Distributions of Faraday rotation measure (FRM) and the projected magnetic
field derived by a 3-dimensional simulation of MHD jets are investigated based
on our "sweeping magnetic twist model". FRM and Stokes parameters were
calculated to be compared with radio observations of large scale wiggled AGN
jets on kpc scales. We propose that the FRM distribution can be used to discuss
the 3-dimensional structure of magnetic field around jets and the validity of
existing theoretical models, together with the projected magnetic field derived
from Stokes parameters. In the previous paper, we investigated the basic
straight part of AGN jets by using the result of a 2-dimensional axisymmetric
simulation. The derived FRM distribution has a general tendency to have a
gradient across the jet axis, which is due to the toroidal component of the
magnetic field generated by the rotation of the accretion disk. In this paper,
we consider the wiggled structure of the AGN jets by using the result of a
3-dimensional simulation. Our numerical results show that the distributions of
FRM and the projected magnetic field have a clear correlation with the large
scale structure of the jet itself, namely, 3-dimensional helix. Distributions,
seeing the jet from a certain direction, show a good matching with those in a
part of 3C449 jet. This suggests that the jet has a helical structure and that
the magnetic field (especially the toroidal component) plays an important role
in the dynamics of the wiggle formation because it is due to a current-driven
helical kink instability in our model.Comment: Accepted for publication in Ap
Recent Advances in Percutaneous Cardioscopy
Percutaneous cardioscopy, using high-resolution fiberoptic imaging, enables direct visualization of the cardiac interior, thereby enabling macroscopic pathological diagnosis. Percutaneous cardioscopy has demonstrated that the endocardial surface exhibits various colors characteristic of different heart diseases. This imaging modality can now be used for evaluation of the severity of myocardial ischemia, and staging of myocarditis. Myocardial blood flow recovery induced by vasodilating agents or percutaneous coronary interventions can be clearly visualized. Morphological and functional changes in the cardiac valves can also be evaluated. Cardioscope-guided endomyocardial biopsy enables pin-point biopsy of the diseased myocardium. Recently, dye-image cardioscopy and fluorescence cardioscopy were developed for evaluation of the subendocardial microcirculation. Cardioscope-guided intracardiac therapies such as myotomy, myectomy, valvulotomy, and transendocardial angiogenic and myogenic therapy have been trialed using animal models in anticipation of future clinical applications. Percutaneous cardioscopy has the potential to contribute to our understanding of heart disease, and to assist in guidance for intracardiac therapies
Bandwidth-disorder phase diagram of half doped layered manganites
Phase diagrams in the plane of (the average ionic radius, related to
one-electron bandwidth ) and (the ionic radius variance,
measuring the quenched disorder), or ``bandwidth-disorder phase diagrams'',
have been established for perovskite manganites, with three-dimensional (3)
Mn-O network. Here we establish the intrinsic bandwidth-disorder phase diagram
of half-doped layered manganites with the two-dimensional (2) Mn-O network,
examining in detail the ``mother state'' of the colossal magnetoresistance
(CMR) phenomenon in crystals without ferromagnetic instability. The
consequences of the reduced dimensionality, from 3 to 2, on the
order-disorder phenomena in the charge-orbital sectors are also highlighted.Comment: REVTeX 4 style; 5 pages, 4 figure
Linear-response theory of the longitudinal spin Seebeck effect
We theoretically investigate the longitudinal spin Seebeck effect, in which
the spin current is injected from a ferromagnet into an attached nonmagnetic
metal in a direction parallel to the temperature gradient. Using the fact that
the phonon heat current flows intensely into the attached nonmagnetic metal in
this particular configuration, we show that the sign of the spin injection
signal in the longitudinal spin Seebeck effect can be opposite to that in the
conventional transverse spin Seebeck effect when the electron-phonon
interaction in the nonmagnetic metal is sufficiently large. Our linear-response
approach can explain the sign reversal of the spin injection signal recently
observed in the longitudinal spin Seebeck effect.Comment: Proc. of ICM 2012 (Accepted for publication in J. Korean Phys. Soc.),
typos correcte
Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei I. Prediction from our Sweeping Magnetic Twist Model
Using the numerical data of MHD simulation for AGN jets based on our
``sweeping magnetic twist model'', we calculated the Faraday rotation measure
(FRM) and the Stokes parameters to compare with observations. We propose that
the FRM distribution can be used to discuss the 3-dimensional structure of
magnetic field around jets, together with the projected magnetic field derived
from the Stokes parameters. In the present paper, we supposed the basic
straight part of AGN jet, and used the data of axisymmetric simulation. The FRM
distribution we derived has a general tendency to have gradient across the jet
axis, which is due to the toroidal component of the helical magnetic field
generated by the rotation of the accretion disk. This kind of gradient in the
FRM distribution is actually observed in some AGN jets (e.g. Asada et al.
2002), which suggests helical magnetic field around the jets and thus supports
our MHD model. Following this success, we are now extending our numerical
observation to the wiggled part of the jets using the data of 3-dimensional
simulation based on our model in the following paper.Comment: Accepted for publication in Ap
Asymmetric Supernovae from Magneto-Centrifugal Jets
Strong toroidal magnetic fields generated in stellar collapse can generate
magneto-centrifugal jets in analogy to those found in simulations of black hole
accretion and explain why all core collapse supernovae are found to be
substantially asymmetric and predominantly bi-polar. We describe two phases:
the initial LeBlanc-Wilson jet and a subsequent protopulsar or toroidal jet
that propagates at about the core escape velocity. The jets will produce bow
shocks that tend to expel matter, including iron and silicon, into equatorial
tori, accounting for observations of the element distribution in Cas A. A
magnetic ``switch'' mechanism may apply in instances of low density and large
magnetic field with subsequent increase in the speed and collimation of the
toroidal jet, depositing relatively little momentum. The result could be enough
infall to form a black hole with a third, highly relativistic jet that could
catch up to the protopulsar jet after it has emerged from the star. The
interaction of these two jets could generate internal shocks and explain the
presence of iron lines in the afterglow. Recent estimates that typical
gamma-ray burst energy is about 3x10^50 erg imply either a very low efficiency
for conversion of rotation into jets, or a rather rapid turnoff of the jet
process even though the black hole still rotates rapidly. Magnetars and
``hypernovae'' might arise in an intermediate parameter regime of energetic
jets that yield larger magnetic fields and provide more energy than the routine
case, but that are not so tightly collimated that they yield failed supernova.
(slightly abridged)Comment: AASTeX, 29 pages, 2 postscript figures, accepted by ApJ, November 20,
200
Coexistence of long-ranged charge and orbital order and spin-glass state in single-layered manganites with weak quenched disorder
The relationship between orbital and spin degrees of freedom in the
single-crystals of the hole-doped PrCaMnO, 0.3
0.7, has been investigated by means of ac-magnetometry and charge
transport. Even though there is no cation ordering on the -site, the
quenched disorder is extremely weak in this system due to the very similar
ionic size of Pr and Ca. A clear asymmetric response of the
system to the under- (respective over-) hole doping was observed. The
long-ranged charge-orbital order established for half doping (=0.5) subsists
in the over-doping case ( 0.5), albeit rearranged to accommodate the
extra holes introduced in the structure. The charge-orbital order is however
destabilized by the presence of extra localized electrons (under-doping,
0.5), leading to its disappearance below =0.35. We show that in an
intermediate under-doped region, with 0.35 0.5, the
``orbital-master spin-slave'' relationship commonly observed in half-doped
manganites does not take place. The long-ranged charge-orbital order is not
accompanied by an antiferromagnetic transition at low temperatures, but by a
frustrated short-ranged magnetic state bringing forth a spin-glass phase. We
discuss in detail the nature and origin of this spin-glass state, which, as in
the half-doped manganites with large quenched disorder, is not related to the
macroscopic phase separation observed in crystals with minor defects or
impurities.Comment: EPL style; 6 pages, 5 figure
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