319 research outputs found
Electronic properties of alkali-metal loaded zeolites -- a "supercrystal" Mott insulator
First-principles band calculations are performed for the first time for an
open-structured zeolite (LTA) with guest atoms (potassium) introduced in their
cages. A surprisingly simple band structure emerges, which indicates that this
system may be regarded as a "supercrystal", where each cluster of guest atoms
with diameter 10\AA acts as a "superatom" with well-defined - and
-like orbitals, which in turn form the bands around the Fermi energy. The
calculated Coulomb and exchange energies for these states turn out to be in the
strongly-correlated regime. With the dynamical mean-field theory we show the
system should be on the Mott-insulator side, and, on a magnetic phase diagram
for degenerate-orbital systems, around the ferromagnetic regime, in accord with
experimental results. We envisage this class of systems can provide a new
avenue for materials design.Comment: 4 pages, 4 figure
High-resolution reconstruction of late Pleistocene climate based on TOC content in a 54m sediment core drilled from Takano Formation, central Japan
The Takano Formation of late Pleistocene lacustrine sediment is distributed at the southern Nagano City. The TKN-2004 core, 53.88 m long, was taken at the central part or the basin, and is composed mostly or homogenous clayey silt. Age of the sediment was estimated from the relationship between radiometric ages and calibrated depths of DKP,Aso-4,K-Tz,Ata and Aso-2tephras, postulating that the sedimentation rate is constant.Paleoclimate from 169ka to 37ka was reconstructed on the basis of TOC content variation. The long-term TOC fluctuations are concordant with the SPECMAP curve. This result is supported by pollen composition. The short-term variations are similar to stadial-interstadial cycles in the Greenland ice cores, and most of warm peaks can be correlated with IS 9 to 25.長野市南部に分布する更新世後期の湖成層である高野層において,全層ボーリングを行い53.88mの連続したコア試料を得た.コア試料は,黒灰色ではぼ均質な粘土質シルト~シルトの層相を示し,多数のテフラ層を挟んでいる.これらのうち5つの広域指標テフラ(DKP,Aso-4,K-Tz, Ata,Aso-2)の放射年代値と補正深度を用いて年代モデルを作成した.高野層のTOC含有率の経年変動は,本コア試料中の花粉組成変化と同調しており,およそ169ka~37kaにおける数万年周期の長期の気候変動を示している.この変動はMIS 6-3前半における海洋酸素同位体比変動と同調しており,各ステージに対比される長期の温暖期・寒冷期が認識できた.また,数百~数千年周期の短期の寒暖変動も存在しており,これらは亜氷期-亜間氷期サイクルに相当すると考えられる.また,それらの温暖期の多くはIS9~25に対比される可能性がある.ArticleJournal of the Sedimentological Society of Japan. 64:37-41 (2007)journal articl
Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu(PO) with CuO square cupolas
In vortex-like spin arrangements, multiple spins can combine into emergent
multipole moments. Such multipole moments have broken space-inversion and
time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME)
activity. Three types of such multipole moments are known: toroidal, monopole,
and quadrupole moments. So far, however, the ME-activity of these multipole
moments has only been established experimentally for the toroidal moment. Here,
we propose a magnetic square cupola cluster, in which four corner-sharing
square-coordinated metal-ligand fragments form a noncoplanar buckled structure,
as a promising structural unit that carries an ME-active multipole moment. We
substantiate this idea by observing clear magnetodielectric signals associated
with an antiferroic ME-active magnetic quadrupole order in the real material
Ba(TiO)Cu(PO). The present result serves as a useful guide for
exploring and designing new ME-active materials based on vortex-like spin
arrangements.Comment: 4 figure
Signatures of the excitonic memory effects in four-wave mixing processes in cavity polaritons
We report the signatures of the exciton correlation effects with finite
memory time in frequency domain degenerate four-wave mixing (DFWM) in
semiconductor microcavity. By utilizing the polarization selection rules, we
discriminate instantaneous, mean field interactions between excitons with the
same spins, long-living correlation due to the formation of biexciton state by
excitons with opposite spins, and short-memory correlation effects in the
continuum of unbound two-exciton states. The DFWM spectra give us the relative
contributions of these effects and the upper limit for the time of the
exciton-exciton correlation in the unbound two-exciton continuum. The obtained
results reveal the basis of the cavity polariton scattering model for the DFWM
processes in high-Q GaAs microcavity.Comment: 11 pages, 1 figur
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
Common carotid intima media thickness and ankle-brachial pressure index correlate with local but not global atheroma burden:a cross sectional study using whole body magnetic resonance angiography
Common carotid intima media thickness (CIMT) and ankle brachial pressure index (ABPI) are used as surrogate marker of atherosclerosis, and have been shown to correlate with arterial stiffness, however their correlation with global atherosclerotic burden has not been previously assessed. We compare CIMT and ABPI with atheroma burden as measured by whole body magnetic resonance angiography (WB-MRA).50 patients with symptomatic peripheral arterial disease were recruited. CIMT was measured using ultrasound while rest and exercise ABPI were performed. WB-MRA was performed in a 1.5T MRI scanner using 4 volume acquisitions with a divided dose of intravenous gadolinium gadoterate meglumine (Dotarem, Guerbet, FR). The WB-MRA data was divided into 31 anatomical arterial segments with each scored according to degree of luminal narrowing: 0 = normal, 1 = <50%, 2 = 50-70%, 3 = 70-99%, 4 = vessel occlusion. The segment scores were summed and from this a standardized atheroma score was calculated.The atherosclerotic burden was high with a standardised atheroma score of 39.5±11. Common CIMT showed a positive correlation with the whole body atheroma score (β 0.32, p = 0.045), however this was due to its strong correlation with the neck and thoracic segments (β 0.42 p = 0.01) with no correlation with the rest of the body. ABPI correlated with the whole body atheroma score (β -0.39, p = 0.012), which was due to a strong correlation with the ilio-femoral vessels with no correlation with the thoracic or neck vessels. On multiple linear regression, no correlation between CIMT and global atheroma burden was present (β 0.13 p = 0.45), while the correlation between ABPI and atheroma burden persisted (β -0.45 p = 0.005).ABPI but not CIMT correlates with global atheroma burden as measured by whole body contrast enhanced magnetic resonance angiography in a population with symptomatic peripheral arterial disease. However this is primarily due to a strong correlation with ilio-femoral atheroma burden
The HY5-PIF regulatory module coordinates light and temperature control of photosynthetic gene transcription
The ability to interpret daily and seasonal alterations in light and temperature signals is essential for plant survival. This is particularly important during seedling establishment when the phytochrome photoreceptors activate photosynthetic pigment production for photoautotrophic growth. Phytochromes accomplish this partly through the suppression of phytochrome interacting factors (PIFs), negative regulators of chlorophyll and carotenoid biosynthesis. While the bZIP transcription factor long hypocotyl 5 (HY5), a potent PIF antagonist, promotes photosynthetic pigment accumulation in response to light. Here we demonstrate that by directly targeting a common promoter cis-element (G-box), HY5 and PIFs form a dynamic activation-suppression transcriptional module responsive to light and temperature cues. This antagonistic regulatory module provides a simple, direct mechanism through which environmental change can redirect transcriptional control of genes required for photosynthesis and photoprotection. In the regulation of photopigment biosynthesis genes, HY5 and PIFs do not operate alone, but with the circadian clock. However, sudden changes in light or temperature conditions can trigger changes in HY5 and PIFs abundance that adjust the expression of common target genes to optimise photosynthetic performance and growth
- …