62 research outputs found
Critical Diagnosis of Electronic Dimensionality Reduction in Semiconductor Quantum Well Structures
Two-dimensional (2D) systems, such as high-temperature superconductors,
surface states of topological insulators, and layered materials, have been
intensively studied using vacuum-ultraviolet (VUV) angle-resolved photoemission
spectroscopy (ARPES). In semiconductor films (heterostructures), quantum well
(QW) states arise due to electron/hole accumulations at the surface
(interface). The quantized states due to quantum confinement can be observed by
VUV-ARPES, while the periodic intensity modulations along the surface normal
(kz) direction of these quantized states are also observable by varying
incident photon energy, resembling three-dimensional (3D) band dispersion. We
have conducted soft X-ray (SX) ARPES measurements on thick and ultrathin III-V
semiconductor InSb(001) films to investigate the electronic dimensionality
reduction in semiconductor QWs. In addition to the dissipation of the kz
dispersion, the SX-ARPES observations demonstrate the changes of the symmetry
and periodicity of the Brillouin zone in the ultrathin film as 2D QW compared
with these of the 3D bulk one, indicating the electronic dimensionality
reduction of the 3D bulk band dispersion caused by the quantum confinement. The
results provide a critical diagnosis using SX-ARPES for the dimensionality
reduction in semiconductor QW structures
Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films
Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too
Conformationally-flexible and moderately electron-donating units-installed D–A–D triad enabling multicolor-changing mechanochromic luminescence, TADF and room-temperature phosphorescence
A novel twisted donor–acceptor–donor (D–A–D) π-conjugated compound that contains flexible and moderately-electron-donating units has been designed and synthesized. It exhibited not only multi-color-changing mechanochromic luminescence and thermally activated delayed fluorescence, but also, unexpectedly, room-temperature phosphorescence in a host layer
Evolution of the Fe-3 impurity band state as the origin of high Curie temperature in p-type ferromagnetic semiconductor (Ga,Fe)Sb
(Ga,Fe)Sb is one of the promising ferromagnetic semiconductors
for spintronic device applications because its Curie temperature ()
is above 300 K when the Fe concentration is equal to or higher than ~0.20.
However, the origin of the high in (Ga,Fe)Sb remains to be
elucidated. To address this issue, we use resonant photoemission spectroscopy
(RPES) and first-principles calculations to investigate the dependence of
the Fe 3 states in (Ga,Fe)Sb ( = 0.05, 0.15, and 0.25) thin
films. The observed Fe 2-3 RPES spectra reveal that the Fe-3 impurity
band (IB) crossing the Fermi level becomes broader with increasing , which
is qualitatively consistent with the picture of double-exchange interaction.
Comparison between the obtained Fe-3 partial density of states and the
first-principles calculations suggests that the Fe-3 IB originates from the
minority-spin () states. The results indicate that enhancement
of the interaction between electrons with increasing is the
origin of the high in (Ga,Fe)Sb
Noise robust automatic charge state recognition in quantum dots by machine learning and pre-processing, and visual explanations of the model with Grad-CAM
Charge state recognition in quantum dot devices is important in preparation
of quantum bits for quantum information processing. Towards auto-tuning of
larger-scale quantum devices, automatic charge state recognition by machine
learning has been demonstrated. In this work, we propose a simpler method using
machine learning and pre-processing. We demonstrate the operation of the charge
state recognition and evaluated an accuracy high as 96%. We also analyze the
explainability of the trained machine learning model by gradient-weighted class
activation mapping (Grad-CAM) which identifies class-discriminative regions for
the predictions. It exhibits that the model predicts the state based on the
change transition lines, indicating human-like recognition is realized.Comment: 15 pages, 6 figure
DOCK2 is involved in the host genetics and biology of severe COVID-19
「コロナ制圧タスクフォース」COVID-19疾患感受性遺伝子DOCK2の重症化機序を解明 --アジア最大のバイオレポジトリーでCOVID-19の治療標的を発見--. 京都大学プレスリリース. 2022-08-10.Identifying the host genetic factors underlying severe COVID-19 is an emerging challenge. Here we conducted a genome-wide association study (GWAS) involving 2, 393 cases of COVID-19 in a cohort of Japanese individuals collected during the initial waves of the pandemic, with 3, 289 unaffected controls. We identified a variant on chromosome 5 at 5q35 (rs60200309-A), close to the dedicator of cytokinesis 2 gene (DOCK2), which was associated with severe COVID-19 in patients less than 65 years of age. This risk allele was prevalent in East Asian individuals but rare in Europeans, highlighting the value of genome-wide association studies in non-European populations. RNA-sequencing analysis of 473 bulk peripheral blood samples identified decreased expression of DOCK2 associated with the risk allele in these younger patients. DOCK2 expression was suppressed in patients with severe cases of COVID-19. Single-cell RNA-sequencing analysis (n = 61 individuals) identified cell-type-specific downregulation of DOCK2 and a COVID-19-specific decreasing effect of the risk allele on DOCK2 expression in non-classical monocytes. Immunohistochemistry of lung specimens from patients with severe COVID-19 pneumonia showed suppressed DOCK2 expression. Moreover, inhibition of DOCK2 function with CPYPP increased the severity of pneumonia in a Syrian hamster model of SARS-CoV-2 infection, characterized by weight loss, lung oedema, enhanced viral loads, impaired macrophage recruitment and dysregulated type I interferon responses. We conclude that DOCK2 has an important role in the host immune response to SARS-CoV-2 infection and the development of severe COVID-19, and could be further explored as a potential biomarker and/or therapeutic target
The whole blood transcriptional regulation landscape in 465 COVID-19 infected samples from Japan COVID-19 Task Force
「コロナ制圧タスクフォース」COVID-19患者由来の血液細胞における遺伝子発現の網羅的解析 --重症度に応じた遺伝子発現の変化には、ヒトゲノム配列の個人差が影響する--. 京都大学プレスリリース. 2022-08-23.Coronavirus disease 2019 (COVID-19) is a recently-emerged infectious disease that has caused millions of deaths, where comprehensive understanding of disease mechanisms is still unestablished. In particular, studies of gene expression dynamics and regulation landscape in COVID-19 infected individuals are limited. Here, we report on a thorough analysis of whole blood RNA-seq data from 465 genotyped samples from the Japan COVID-19 Task Force, including 359 severe and 106 non-severe COVID-19 cases. We discover 1169 putative causal expression quantitative trait loci (eQTLs) including 34 possible colocalizations with biobank fine-mapping results of hematopoietic traits in a Japanese population, 1549 putative causal splice QTLs (sQTLs; e.g. two independent sQTLs at TOR1AIP1), as well as biologically interpretable trans-eQTL examples (e.g., REST and STING1), all fine-mapped at single variant resolution. We perform differential gene expression analysis to elucidate 198 genes with increased expression in severe COVID-19 cases and enriched for innate immune-related functions. Finally, we evaluate the limited but non-zero effect of COVID-19 phenotype on eQTL discovery, and highlight the presence of COVID-19 severity-interaction eQTLs (ieQTLs; e.g., CLEC4C and MYBL2). Our study provides a comprehensive catalog of whole blood regulatory variants in Japanese, as well as a reference for transcriptional landscapes in response to COVID-19 infection
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