11,102 research outputs found
The Dense Plasma Torus Around the Nucleus of an Active Galaxy NGC 1052
A subparsec-scale dense plasma torus around an active galactic nucleus (AGN)
is unveiled. We report on very-long-baseline interferometry (VLBI) observations
at 2.3, 8.4, and 15.4 GHz towards the active galaxy NGC 1052. The convex
spectra of the double-sided jets and the nucleus imply that synchrotron
emission is obscured through free--free absorption (FFA) by the foreground cold
dense plasma. A trichromatic image was produced to illustrate the distribution
of the FFA opacity. We found a central condensation of the plasma which covers
about 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. A
simple explanation for the asymmetric distribution is the existence of a thick
plasma torus perpendicular to the jets. We also found an ambient FFA absorber,
whose density profile can be ascribed to a spherical distribution of the
isothermal King model. The coexistence of torus-like and spherical
distributions of the plasma suggests a transition from radial accretion to
rotational accretion around the nucleus.Comment: 10 pages, to appear in Publ. Astron. Soc. Japan, vol.53, No.2 (2001
Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation
Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose
electronic properties within a localized ion picture are characterized by
non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical
frustration, has been investigated by muon spin rotation/relaxation (muSR)
technique. The A cation (mostly divalent) was varied to examine the effect of
covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg
that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is
associated with a weak structural transition), a nearly commensurate magnetic
order is observed to develop in accordance with the MI transition. Meanwhile,
in the case of A = Cd where the MI transition is suppressed to the level of
small anomaly in the resistivity, the local field distribution probed by muon
indicates emergence of a certain magnetic inhomogeneity below {\guillemotright}
30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly
inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru
moments and thus described as a "frozen spin liquid" state. The systematic
trend of increasing randomness and itinerant character with decreasing
covalency suggests close relationship between these two characters. As a
reference for the effect of orbital degeneracy and associated Jahn-Teller
instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+,
4d4), where the result of muSR indicates a non-magnetic ground state that is
consistent with the formation of the Haldane chains suggested by neutron
diffraction experiment.Comment: 12 pages, 13 figure
An Efficient Algorithm for Enumerating Chordless Cycles and Chordless Paths
A chordless cycle (induced cycle) of a graph is a cycle without any
chord, meaning that there is no edge outside the cycle connecting two vertices
of the cycle. A chordless path is defined similarly. In this paper, we consider
the problems of enumerating chordless cycles/paths of a given graph
and propose algorithms taking time for each chordless cycle/path. In
the existing studies, the problems had not been deeply studied in the
theoretical computer science area, and no output polynomial time algorithm has
been proposed. Our experiments showed that the computation time of our
algorithms is constant per chordless cycle/path for non-dense random graphs and
real-world graphs. They also show that the number of chordless cycles is much
smaller than the number of cycles. We applied the algorithm to prediction of
NMR (Nuclear Magnetic Resonance) spectra, and increased the accuracy of the
prediction
Quantum network coding for quantum repeaters
This paper considers quantum network coding, which is a recent technique that
enables quantum information to be sent on complex networks at higher rates than
by using straightforward routing strategies. Kobayashi et al. have recently
showed the potential of this technique by demonstrating how any classical
network coding protocol gives rise to a quantum network coding protocol. They
nevertheless primarily focused on an abstract model, in which quantum resource
such as quantum registers can be freely introduced at each node. In this work,
we present a protocol for quantum network coding under weaker (and more
practical) assumptions: our new protocol works even for quantum networks where
adjacent nodes initially share one EPR-pair but cannot add any quantum
registers or send any quantum information. A typically example of networks
satisfying this assumption is {\emph{quantum repeater networks}}, which are
promising candidates for the implementation of large scale quantum networks.
Our results thus show, for the first time, that quantum network coding
techniques can increase the transmission rate in such quantum networks as well.Comment: 9 pages, 11figure
A comparison and a combination of SST and AGM algorithms for counting points of elliptic curves in characteristic 2
International audienceSince the first use of a p-adic method for counting points of elliptic curves, by Satoh in 1999, several variants of his algorithm have been proposed. In the current state, the AGM algorithm, proposed by Mestre is thought to be the fastest in practice, and the algorithm by Satoh-Skjernaa-Taguchi has the best asymptotic complexity but requires precomputations. We present an amelioration of the SST algorithm, borrowing ideas from the AGM. We make a precise comparison between this modified SST algorithm and the AGM, thus demonstrating that the former is faster by a significant factor, even for small cryptographic sizes
Impurity migration and diffusion during deformation-induced recrystallization of ice
第3回極域科学シンポジウム/第35回極域気水圏シンポジウム 11月29日(木) 国立国語研究所 2階ロビ
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