2,525 research outputs found
Multicriticality of the (2+1)-dimensional gonihedric model: A realization of the (d,m)=(3,2) Lifshitz point
Multicriticality of the gonihedric model in 2+1 dimensions is investigated
numerically. The gonihedric model is a fully frustrated Ising magnet with the
finely tuned plaquette-type (four-body and plaquette-diagonal) interactions,
which cancel out the domain-wall surface tension. Because the
quantum-mechanical fluctuation along the imaginary-time direction is simply
ferromagnetic, the criticality of the (2+1)-dimensional gonihedric model should
be an anisotropic one; that is, the respective critical indices of real-space
(\perp) and imaginary-time (\parallel) sectors do not coincide. Extending the
parameter space to control the domain-wall surface tension, we analyze the
criticality in terms of the crossover (multicritical) scaling theory. By means
of the numerical diagonalization for the clusters with N\le 28 spins, we
obtained the correlation-length critical indices
(\nu_\perp,\nu_\parallel)=(0.45(10),1.04(27)), and the crossover exponent
\phi=0.7(2). Our results are comparable to
(\nu_{\perp},\nu_{\parallel})=(0.482,1.230), and \phi=0.688 obtained by Diehl
and Shpot for the (d,m)=(3,2) Lifshitz point with the \epsilon-expansion method
up to O(\epsilon^2)
XAFS analyses of molten metal fluorides
X-ray absorption fine structure studies of molten metal fluorides containing the materials related to nuclear engineering are intensively summarized. By using XAFS spectra data of divalent and trivalent cation metal fluorides in molten state which have been collected by authors’ group for a few years, local structure have been extracted and discussed systematically in conjunction with other spectroscopic studies and numerical calculations. In molten divalent fluorides, tetrahedral coordination of fluorides around a cation is predominant. In the case of pure molten trivalent fluorides, structure with more than 6-coordination has been suggested in some cases, but octahedral coordination structure is much stabilized at heavier rare earth metal fluorides. By mixing with alkali metal fluorides, it is a general trend that inter-ionic distances keep constant, but coordination number of fluorides decreases. In experimental chapter, all the details of sample preparation, furnace installation, X-ray optics setups and data analyses procedures are explained. Finally, future expectations of XAFS technique are also suggested
Abelian dominance and the dual Meissner effect in local unitary gauges in SU(2) gluodynamics
Performing highly precise Monte-Carlo simulations of SU(2) gluodynamics, we
observe for the first time Abelian dominance in the confining part of the
static potential in local unitary gauges such as the F12 gauge. We also study
the flux-tube profile between the quark and antiquark in these local unitary
gauges and find a clear signal of the dual Meissner effect. The Abelian
electric field is found to be squeezed into a flux tube by the monopole
supercurrent. This feature is the same as that observed in the non-local
maximally Abelian gauge. These results suggest that the Abelian confinement
scenario is gauge independent. Observing the important role of space-like
monopoles in the Polyakov gauge also indicates that the monopoles defined on
the lattice do not necessarily correspond to those proposed by 't Hooft in the
context of Abelian projection.Comment: 4 pages, 7 figure
Suzaku Observations of Active Galactic Nuclei Detected in the Swift/BAT Survey: Discovery of "New Type" of Buried Supermassive Black Holes
We present the Suzaku broad band observations of two AGNs detected by the
Swift/BAT hard X-ray (>15 keV) survey that did not have previous X-ray data,
Swift J0601.9-8636 and Swift J0138.6-4001. The Suzaku spectra reveals in both
objects a heavily absorbed power law component with a column density of NH =~
10^{23.5-24} cm^{-2} that dominates above 10 keV, and an intense reflection
component with a solid angle >~ from a cold, optically thick medium. We
find that these AGNs have an extremely small fraction of scattered light from
the nucleus, <~ 0.5% with respect to the intrinsic power law component. This
indicates that they are buried in a very geometrically-thick torus with a small
opening angle and/or have unusually small amount of gas responsible for
scattering. In the former case, the geometry of Swift J0601.9-8636 should be
nearly face-on as inferred from the small absorption for the reflection
component. The discovery of two such objects in this small sample implies that
there must be a significant number of yet unrecognized, very Compton thick AGNs
viewed at larger inclination angles in the local universe, which are difficult
to detect even in the currently most sensitive optical or hard X-ray surveys.Comment: 4 pages, 3 figures, accepted for publication in ApJ Lette
The ASCA Medium Sensitivity Survey (the GIS Catalog Project): Source Counts and Evidence for Emerging Population of Hard Sources
We present first results from the ASCA Medium Sensitivity Survey (AMSS; or
the GIS catalog project). From the serendipitous fields amounting to 106
degE-2, we determined the Log N - Log S relations in the 0.7-7 keV and 2-10 keV
bands with the best statistical accuracy obtained so far, over the flux range
from 1 x 10E-11 to 5 x 10E-14 and 7 x 10E-14 erg sE-1 cmE-2, respectively. When
the sources detected in the 0.7-7 keV band are divided into two subsamples with
higher and lower spectral hardness, the former exhibits a significantly steeper
slope than the latter at fluxes below ~10E-12 erg sE-1 cmE-2 (0.7-7 keV). The
average spectrum of sources becomes continuously harder toward fainter fluxes,
from a photon index of 2.1 in the 0.7-10 keV range at the flux of ~10E-11 to
1.6 at ~10E-13 erg sE-1 cmE-2 (0.7-7 keV). This is consistent with the
comparison of source counts between the 2-10 keV and the 0.7-2 keV band, and
solves the puzzle of their discrepancy reported previously. Our results
demonstrate rapid emergence of hard X-ray sources with a decreasing flux from
\~10E-12 to ~10E-13 erg sE-1 cmE-2 (2-10 keV).Comment: 10 pages, 3 figures (including 2 color figures). Accepted for
publication in ApJ
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