436 research outputs found
Two-Dimensional Topological Insulator State and Topological Phase Transition in Bilayer Graphene
We show that gated bilayer graphene hosts a strong topological insulator (TI)
phase in the presence of Rashba spin-orbit (SO) coupling. We find that gated
bilayer graphene under preserved time-reversal symmetry is a quantum valley
Hall insulator for small Rashba SO coupling , and
transitions to a strong TI when ,
where and are respectively the interlayer potential and tunneling
energy. Different from a conventional quantum spin Hall state, the edge modes
of our strong TI phase exhibit both spin and valley filtering, and thus share
the properties of both quantum spin Hall and quantum valley Hall insulators.
The strong TI phase remains robust in the presence of weak graphene intrinsic
SO coupling.Comment: 5 pages and 4 figure
Topological phases in gated bilayer graphene: Effects of Rashba spin-orbit coupling and exchange field
We present a systematic study on the influence of Rashba spin-orbit coupling,
interlayer potential difference and exchange field on the topological
properties of bilayer graphene. In the presence of only Rashba spin-orbit
coupling and interlayer potential difference, the band gap opening due to
broken out-of-plane inversion symmetry offers new possibilities of realizing
tunable topological phase transitions by varying an external gate voltage. We
find a two-dimensional topological insulator phase and a quantum valley
Hall phase in -stacked bilayer graphene and obtain their effective
low-energy Hamiltonians near the Dirac points. For stacking, we do not
find any topological insulator phase in the presence of large Rashba spin-orbit
coupling. When the exchange field is also turned on, the bilayer system
exhibits a rich variety of topological phases including a quantum anomalous
Hall phase, and we obtain the phase diagram as a function of the Rashba
spin-orbit coupling, interlayer potential difference, and exchange field.Comment: 15 pages, 17figures, and 1 tabl
Quantum Anomalous Hall Effect in Graphene from Rashba and Exchange Effects
We investigate the possibility of realizing quantum anomalous Hall effect in
graphene. We show that a bulk energy gap can be opened in the presence of both
Rashba spin-orbit coupling and an exchange field. We calculate the Berry
curvature distribution and find a non-zero Chern number for the valence bands
and demonstrate the existence of gapless edge states. Inspired by this finding,
we also study, by first principles method, a concrete example of graphene with
Fe atoms adsorbed on top, obtaining the same result.Comment: 4 papges, 5 figure
Isolation and identification of potent antidiabetic compounds from Antrodia cinnamomea - An edible Taiwanese mushroom
[[abstract]]Antrodia cinnamomea (AC), an edible Taiwanese mushroom, has been recognized as a
valuable natural resource with vast biological and medicinal benefits. Recently, the hypoglycemic and
anti-diabetic effects of AC were mentioned in several studies. However, no studies have investigated
α-glucosidase inhibitors from AC fruiting bodies (ACFB) as they relate to type 2 diabetes (T2D)
treatment. The purpose of this study was to gain evidence of potent α-glucosidase inhibitory effects,
as well as isolate, identify and characterize the active compounds of ACFB. The MeOH extract
of ACFB demonstrated potent α-glucosidase inhibitory activity, and possessed high pH stability
(pH 2–11) and thermostable properties at 40–50 ◦C. Further purification led to the isolation of eight
constituents from ACFB, identified as: 25S-antcin K (1), 25R-antcin K (2), dehydrosulphurenic acid
(3), 25S-antcin I (4), 25S-antcin B (5), 25R-antcin B (6), dehydroeburicoic acid (7) and eburicoic acid
(8). Notably, the ACFB extract and its identified compounds, except 1, 4, and 6 demonstrated a
greater effect (EC50 = 0.025–0.21 mg/mL) than acarbose (EC50 = 0.278 mg/mL). As such, these active
compounds were determined to be new potent mushroom α-glucosidase inhibitors. These active
compounds were also identified on the HPLC fingerprints of ACFB.[[sponsorship]]MOST[[notice]]補æ£å®Œ
Quantum Anomalous Hall Effect in Single-layer and Bilayer Graphene
The quantum anomalous Hall effect can occur in single and few layer graphene
systems that have both exchange fields and spin-orbit coupling. In this paper,
we present a study of the quantum anomalous Hall effect in single-layer and
gated bilayer graphene systems with Rashba spin-orbit coupling. We compute
Berry curvatures at each valley point and find that for single-layer graphene
the Hall conductivity is quantized at , with each valley
contributing a unit conductance and a corresponding chiral edge state. In
bilayer graphene, we find that the quantized anomalous Hall conductivity is
twice that of the single-layer case when the gate voltage is smaller than
the exchange field , and zero otherwise. Although the Chern number vanishes
when , the system still exhibits a quantized valley Hall effect, with
the edge states in opposite valleys propagating in opposite directions. The
possibility of tuning between different topological states with an external
gate voltage suggests possible graphene-based spintronics applications.Comment: 9 pages, final published versio
Self-supervised learning-based general laboratory progress pretrained model for cardiovascular event detection
The inherent nature of patient data poses several challenges. Prevalent cases
amass substantial longitudinal data owing to their patient volume and
consistent follow-ups, however, longitudinal laboratory data are renowned for
their irregularity, temporality, absenteeism, and sparsity; In contrast,
recruitment for rare or specific cases is often constrained due to their
limited patient size and episodic observations. This study employed
self-supervised learning (SSL) to pretrain a generalized laboratory progress
(GLP) model that captures the overall progression of six common laboratory
markers in prevalent cardiovascular cases, with the intention of transferring
this knowledge to aid in the detection of specific cardiovascular event. GLP
implemented a two-stage training approach, leveraging the information embedded
within interpolated data and amplify the performance of SSL. After GLP
pretraining, it is transferred for TVR detection. The proposed two-stage
training improved the performance of pure SSL, and the transferability of GLP
exhibited distinctiveness. After GLP processing, the classification exhibited a
notable enhancement, with averaged accuracy rising from 0.63 to 0.90. All
evaluated metrics demonstrated substantial superiority (p < 0.01) compared to
prior GLP processing. Our study effectively engages in translational
engineering by transferring patient progression of cardiovascular laboratory
parameters from one patient group to another, transcending the limitations of
data availability. The transferability of disease progression optimized the
strategies of examinations and treatments, and improves patient prognosis while
using commonly available laboratory parameters. The potential for expanding
this approach to encompass other diseases holds great promise.Comment: published in IEEE Journal of Translational Engineering in Health &
Medicin
Ultrafast High-Energy Micro-Supercapacitors Based On Open-Shell Polymer-Graphene Composites
Micro-supercapacitors are poised to serve as on-chip power sources for electronics. However, the challenge to simultaneously increase their power, energy, and lifetime demands new material combinations beyond current carbon-based systems. Here, we demonstrate that electro-deposition of an open-shell conjugated polymer with reduced graphene oxide achieves electrodes with capacitance up to 186 mF cm−2 (372 F cm−3). The extended delocalization within the open-shell polymer stabilizes redox states and facilitates a 3 V wide potential window, while the hierarchical electrode structure promotes ultrafast kinetics. The micro-supercapacitor shows a high power density of 227 mW cm−2 with an energy density of 10.5 μWh cm−2 and stability of 84% capacitance retention after 11,000 cycles. These attributes allow operation at 120 Hz for fast charging and alternating current (AC) line filtering applications, which may be suitable to replace bulky electrolytic capacitors or serve as high-endurance energy storage for wireless electronics
Bioactivity-guided purification of novel herbal antioxidant and anti-NO compounds from Euonymus laxiflorus Champ
[[abstract]]Euonymus laxiflorus Champ., a medicinal herb collected in Vietnam, has been reported
to show several potent bioactivities, including anti-NO, enzyme inhibition, hypoglycemic and
antidiabetic effects. Recently, the antioxidant activity of Euonymus laxiflorus Champ. trunk bark
(ELCTB) has also been reported. However, the active antioxidant and anti-NO constituents existing
in ELCTB have not been reported in the literature. The objective of this study was to purify the active
antioxidants from ELCTB and investigate the anti-NO effect of the major constituents. Twenty-two
phenolics isolated from ELCTB, including 12 compounds newly isolated in this study (1–12) and
10 constituents obtained from our previous work, were evaluated for their antioxidant activity.
Of these, 12 compounds (4–6, 9, 13–15, 18–22) showed a potent antioxidant capacity (FRS50 =
7.8–58.11 µg/mL), in comparison to α-tocopherol (FRS50 = 23 µg/mL). In the anti-NO activity tests,
Walterolactone A (1a) and B (1b) β-D-glucopyranoside (13) demonstrated the most effective and
comparable activity to that of quercetin with max inhibition and IC50 values of 100%, 1.3 µg/mL, and
100%, 1.21 µg/mL, respectively. The crude extract and its major compounds showed no cytotoxicity
on normal cells. Notably, three constituents (9, 11, and 12) were identified as new compounds,
another three constituents, including 1, 7, and 8, were found to be new natural products, constituents
9 and 13 were determined to be new antioxidants, and compound 13 was reported to have novel
potent anti-NO activity for the first time. The results of this study contribute to the enrichment of
new natural products and compounds, as well as the novel biological activity of constituents isolated
from Euonymus laxiflorus Champ. The current study also indicates ELCTB as a rich natural source of
active phenolics. It is suggested that ELCTB could be developed as a health food with promising
antioxidant and anti-NO effects, as well as other beneficial biological activities.[[sponsorship]]科技部[[notice]]補æ£å®Œ
Intrinsic Correlation between Hardness and Elasticity in Polycrystalline Materials and Bulk Metallic Glasses
Though extensively studied, hardness, defined as the resistance of a material
to deformation, still remains a challenging issue for a formal theoretical
description due to its inherent mechanical complexity. The widely applied
Teter's empirical correlation between hardness and shear modulus has been
considered to be not always valid for a large variety of materials. Here,
inspired by the classical work on Pugh's modulus ratio, we develop a
theoretical model which establishes a robust correlation between hardness and
elasticity for a wide class of materials, including bulk metallic glasses, with
results in very good agreement with experiment. The simplified form of our
model also provides an unambiguous theoretical evidence for Teter's empirical
correlation.Comment: 10 pages, 4 figures and 3 table
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