1,237 research outputs found
Study of gauge (in)dependence of monopole dynamics
We investigated the gauge (in)dependence of the confinement mechanism due to
monopole condensation in SU(2) lattice QCD by various abelian projections. We
found (1) the string tension can be reproduced by monopoles alone also in
Polyakov gauge and (2) the behaviors of the Polyakov loop at the critical
temperature seem to be explained by the uniformity breaking of the monopole
currents in every gauge.Comment: 4pages (7 figures), Latex, Contribution to Lattice 9
Efficient host excitation in thiosilicate phosphors of lanthanide(III)-doped Y4(SiS4)3
Lanthanide (Ln)-doped yttrium thiosilicate (Y1−x Ln x )4(SiS4)3 is synthesized, and its optical properties are studied. In (Y1−x Tb x )4(SiS4)3, the green photoluminescence band corresponding to the intra 4f transition of 5D4 → 7F5 appears at 545 nm and becomes the maximum for x = 0.2 in the range x = 0.01 to 1. The internal quantum efficiency is higher (11% for x = 0.01) for the thiosilicate host excitation (360 nm) than for the direct excitation (1.6%) of the intra 4f transition of 5D4 ← 7F6 (489 nm). A time-resolved photoluminescence study shows that the luminescence of defect states of thiosilicate hosts decays faster (typically 10–30 ns) for higher Tb3+ concentration x. In addition, the rise time of Tb3+ photoluminescence is shorter (10–40 ns) for greater x. Energy transfer from the thiosilicate host to Tb3+ is discussed using these results. For all of (Y1−x Ln x )4(SiS4)3 (x = 0.01, Ln = Pr, Nd, Dy, Er or Tm), the internal quantum efficiency is higher for the host excitation (11–21%) than for the direct excitation of intra 4f transitions (1.1–12%). A photoluminescence excitation study reveals broad host absorption in 300–400 nm for Ln luminescence. These results show the promising characteristics of the host absorption of (Y1−x Ln x )4(SiS4)3 phosphors and their optical properties
Semileptonic Decay of -Meson into and the Bjorken Sum Rule
We study the semileptonic branching fraction of -meson into higher
resonance of charmed meson by using the Bjorken sum rule and the heavy
quark effective theory(HQET). This sum rule and the current experiment of
-meson semileptonic decay into and predict that the branching
ratio into is about 1.7\%. This predicted value is larger than
the value obtained by the various theoretical hadron models based on the HQET.Comment: 10 pages, LaTex, to be published in Phys. Lett.
Quadrupole moments in chiral material DyFe3(BO3)4 observed by resonant x-ray diffraction
By means of circularly polarized x-ray beam at Dy L3 and Fe K absorption
edges, the chiral structure of the electric quadrupole was investigated for a
single crystal of DyFe3(BO3)4 in which both Dy and Fe ions are arranged in
spiral manners. The integrated intensity of the resonant x- ray diffraction of
space-group forbidden reflections 004 and 005 is interpreted within the
electric dipole transitions from Dy 2p3 to 5d and Fe 1s to 4p, respectively. We
have confirmed that the 2 handedness of the crystal observed at Dy L3 and Fe K
edges is consistent with that observed at Dy M5 edge in the previous study. By
analyzing the azimuth scans of the diffracted intensity, the electronic
quadrupole moments of Dy 5d and Fe 4p are derived. The temperature profiles of
the integrated intensity of 004 at the Dy L3 and the Fe K edges are similar to
those of Dy-O and Fe-O bond lengths, while that at the Dy M5 edge does not. The
results indicate that the helix chiral orientations of quadrupole moments due
to Dy 5d and Fe 4p electrons are more strongly affected by the crystal fields
than Dy 4f
Reconfiguring k-Path Vertex Covers
A vertex subset I of a graph G is called a k-path vertex cover if every path on k vertices in G contains at least one vertex from I. The K-PATH VERTEX COVER RECONFIGURATION (K-PVCR) problem asks if one can transform one k-path vertex cover into another via a sequence of k-path vertex covers where each intermediate member is obtained from its predecessor by applying a given reconfiguration rule exactly once. We investigate the computational complexity of K-PVCR from the viewpoint of graph classes under the well-known reconfiguration rules: TS, TJ, and TAR. The problem for k=2, known as the VERTEX COVER RECONFIGURATION (VCR) problem, has been well-studied in the literature. We show that certain known hardness results for VCR on different graph classes can be extended for K-PVCR. In particular, we prove a complexity dichotomy for K-PVCR on general graphs: on those whose maximum degree is three (and even planar), the problem is PSPACE-complete, while on those whose maximum degree is two (i.e., paths and cycles), the problem can be solved in polynomial time. Additionally, we also design polynomial-time algorithms for K-PVCR on trees under each of TJ and TAR. Moreover, on paths, cycles, and trees, we describe how one can construct a reconfiguration sequence between two given k-path vertex covers in a yes-instance. In particular, on paths, our constructed reconfiguration sequence is shortest
Reconfiguring k-path vertex covers
A vertex subset of a graph is called a -path vertex cover if every
path on vertices in contains at least one vertex from . The
\textsc{-Path Vertex Cover Reconfiguration (-PVCR)} problem asks if one
can transform one -path vertex cover into another via a sequence of -path
vertex covers where each intermediate member is obtained from its predecessor
by applying a given reconfiguration rule exactly once. We investigate the
computational complexity of \textsc{-PVCR} from the viewpoint of graph
classes under the well-known reconfiguration rules: ,
, and . The problem for , known as the
\textsc{Vertex Cover Reconfiguration (VCR)} problem, has been well-studied in
the literature. We show that certain known hardness results for \textsc{VCR} on
different graph classes including planar graphs, bounded bandwidth graphs,
chordal graphs, and bipartite graphs, can be extended for \textsc{-PVCR}. In
particular, we prove a complexity dichotomy for \textsc{-PVCR} on general
graphs: on those whose maximum degree is (and even planar), the problem is
-complete, while on those whose maximum degree is (i.e.,
paths and cycles), the problem can be solved in polynomial time. Additionally,
we also design polynomial-time algorithms for \textsc{-PVCR} on trees under
each of and . Moreover, on paths, cycles, and
trees, we describe how one can construct a reconfiguration sequence between two
given -path vertex covers in a yes-instance. In particular, on paths, our
constructed reconfiguration sequence is shortest.Comment: 29 pages, 4 figures, to appear in WALCOM 202
- …