34 research outputs found
Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets
Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of
coupled alternating chains on a square lattice are investigated by means of the
quantum Monte Carlo method. It is found that, in contrast with the site-diluted
system having an infinitesimal critical concentration, the bond-diluted system
has a finite critical concentration of diluted bonds, , above which the
system is in an antiferromagnetic (AF) long-range ordered phase. In the
disordered phase below , plausibly in the concentration region
significantly less than , the system has a spin gap due to singlet pairs
of induced magnetic moments reformed by the AF interactions through the
two-dimensional shortest paths.Comment: 4 pages, 4 figure
Site-Dilution-Induced Antiferromagnetic Long-Range Order in Two-Dimensional Spin-Gapped Heisenberg Antiferromagnet
Effects of the site dilution on spin-gapped Heisenberg antiferromagnets with
and S=1 on a square lattice are investigated by means of the quantum
Monte Carlo method. It is found that effective magnetic moments induced around
the diluted sites exhibit the antiferromagnetic long-range order in the medium
of spin-singlet pairs. Their microscopic structure is examined in detail and
important roles of the higher dimensionality than one on the phenomenon are
discussed.Comment: RevTeX, 4 pages, 6 figure
2006ネン ニ トクシマシ シロヤマ ニ ショクジュ サレタ ホルトノキ ノ ナエギ ノ ゲンジョウ : セイイク ジョウキョウ ト ホルトノキ イオウビョウ カンセン ジョウキョウ ニツイテ
Elaeocarpus zollingeri (synonym: E. sylvestris) was one of dominant trees in Mt. Shiroyama in the Tokushima City until 1970s, however, most of adult trees have died by Elaeocarpus yellows. To prevent extinction 300 nursery trees were planted at the foot of the mountain by local volunteers in 2006. In this study we investigated their survival, growth, and infection status of the disease. We found 40 nursery trees have survived (survival rate was 13%). Survived trees were abundant in areas facing the south, and most trees disappeared in areas facing the north and the west. Growth of the trees was well also in areas facing the south. Among the survived 40 nursery trees, we found three trees infected with phytoplasma, the pathogen of Elaeocarpus yellows, based on PCR analysis. It is not clear when they were infected with phytoplasma, whether they have infected after the plantation or they already had phytoplasma in the seed. Anyway, the fact that only a few tree is infected must be gratifying in considering the conservation E. zollinger in Mt. Shiroyama
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte