16 research outputs found
Magnetoresistance and spin polarization in the insulating regime of a Si two-dimensional electron system
We have studied the magnetoresistance in a high-mobility Si inversion layer
down to low electron concentrations at which the longitudinal resistivity
has an activated temperature dependence. The angle of the magnetic
field was controlled so as to study the orbital effect proportional to the
perpendicular component for various total strengths . A
dip in , which corresponds to the Landau level filling factor of
, survives even for high resistivity of at
. The linear -dependence of the value of
at the dip for low indicates that a ferromagnetic
instability does not occur even in the far insulating regime.Comment: 6 pages, 7 figures, submitted to PR
Well-width dependence of valley splitting in Si/SiGe quantum wells
The valley splitting in Si two-dimensional electron systems is studied using
Si/SiGe single quantum wells (QWs) with different well widths. The energy gaps
for 4 and 5.3 nm QWs, obtained from the temperature dependence of the
longitudinal resistivity at the Landau level filling factor , are much
larger than those for 10 and 20 nm QWs. This is consistent with the well-width
dependence of the bare valley splitting estimated from the comparison with the
Zeeman splitting in the Shubnikov-de Haas oscillations.Comment: 3 pages, 2 figure
Insulating Phases Induced by Crossing of Partially Filled Landau Levels in a Si Quantum Well
We study magnetotransport in a high mobility Si two-dimensional electron
system by in situ tilting of the sample relative to the magnetic field. A
pronounced dip in the longitudinal resistivity is observed during the Landau
level crossing process for noninteger filling factors. Together with a Hall
resistivity change which exhibits the particle-hole symmetry, this indicates
that electrons or holes in the relevant Landau levels become localized at the
coincidence where the pseudospin-unpolarized state is expected to be stable.Comment: 4 pages, 4 figure
Electronic Transport Properties of the Ising Quantum Hall Ferromagnet in a Si Quantum Well
Magnetotransport properties are investigated for a high mobility Si two
dimensional electron systems in the vicinity of a Landau level crossing point.
At low temperatures, the resistance peak having a strong anisotropy shows large
hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak
is split into two peaks in the paramagnetic regime. A mean field calculation
for the peak positions indicates that electron scattering is strong when the
pseudospin is partially polarized. We also study the current-voltage
characteristics which exhibit a wide voltage plateau.Comment: 4 pages, 4 figure
Effect of amines as activators on the alcohol-oxidizing activity of pyrroloquinoline quinone-dependent quinoprotein alcohol dehydrogenase
Development of cardanol-bonded cellulose thermoplastics: high productivity achieved in two-step heterogeneous process
Diversity and composition of flower-visiting insects and related factors in three fruit tree species
Animal-mediated pollination is an essential ecosystem service for the production of many fruit trees. To reveal the community composition of flower-visiting wild insects which potentially contribute to fruit production and to examine the effects of geographic location, local meteorological conditions and locally introduced domesticated pollinators on them, we investigated the community composition of insects visiting the flowers (hereafter, “visitors”) of apple, Japanese pear and Oriental persimmon for 1‒3 years at 20 sites around Japan. While most of the variation (82%) of the community composition was explained by tree species with a slight contribution by geographic distance (2%), maximum temperature and tree species contributed 62% and 41% of the variation in total abundance of the visitors, respectively. Though the dominant families of the visitors varied spatiotemporally, the community composition of the visitors of apple and Japanese pear clearly differed from that of Oriental persimmon. While Andrenidae and Syrphidae together accounted for 46%‒64% of the visitors of apple and Japanese pear, Apidae represented 57% of the visitors of Oriental persimmon. The taxonomic richness, diversity and evenness of the visitors were best predicted by locally introduced domesticated pollinators and local meteorological conditions of wind speed and maximum temperature. Amongst these selected factors, locally introduced domesticated pollinators could have the largest impact. It seemed to be strongly related to the reduction of taxonomic richness, diversity and evenness of the visitors, accounting for 41‒89% of the variation. Results suggested that the community composition and total abundance of potential pollinators were predominantly determined by tree species and temperature, but locally introduced domesticated pollinators could have a determinantal pressure on the taxonomic diversity of the community
Diversity and composition of flower-visiting insects and related factors in three fruit tree species
Animal-mediated pollination is an essential ecosystem service for the production of many fruit trees. To reveal the community composition of flower-visiting wild insects which potentially contribute to fruit production and to examine the effects of geographic location, local meteorological conditions and locally introduced domesticated pollinators on them, we investigated the community composition of insects visiting the flowers (hereafter, “visitors”) of apple, Japanese pear and Oriental persimmon for 1‒3 years at 20 sites around Japan. While most of the variation (82%) of the community composition was explained by tree species with a slight contribution by geographic distance (2%), maximum temperature and tree species contributed 62% and 41% of the variation in total abundance of the visitors, respectively. Though the dominant families of the visitors varied spatiotemporally, the community composition of the visitors of apple and Japanese pear clearly differed from that of Oriental persimmon. While Andrenidae and Syrphidae together accounted for 46%‒64% of the visitors of apple and Japanese pear, Apidae represented 57% of the visitors of Oriental persimmon. The taxonomic richness, diversity and evenness of the visitors were best predicted by locally introduced domesticated pollinators and local meteorological conditions of wind speed and maximum temperature. Amongst these selected factors, locally introduced domesticated pollinators could have the largest impact. It seemed to be strongly related to the reduction of taxonomic richness, diversity and evenness of the visitors, accounting for 41‒89% of the variation. Results suggested that the community composition and total abundance of potential pollinators were predominantly determined by tree species and temperature, but locally introduced domesticated pollinators could have a determinantal pressure on the taxonomic diversity of the community