180 research outputs found
Single-layer behavior and slow carrier density dynamic of twisted graphene bilayer
We report scanning tunneling microscopy (STM) and spectroscopy (STS) of
twisted graphene bilayer on SiC substrate. For twist angle ~ 4.5o the Dirac
point ED is located about 0.40 eV below the Fermi level EF due to the electron
doping at the graphene/SiC interface. We observed an unexpected result that the
local Dirac point around a nanoscaled defect shifts towards the Fermi energy
during the STS measurements (with a time scale about 100 seconds). This
behavior was attributed to the decoupling between the twisted graphene and the
substrate during the measurements, which lowers the carrier density of graphene
simultaneously
A Triple-Network Dynamic Connection Study in Alzheimer's Disease
© 2022 Meng, Wu, Liang, Zhang, Xu, Yang and Meng. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY). https://creativecommons.org/licenses/by/4.0/Alzheimer's disease (AD) was associated with abnormal organization and function of large-scale brain networks. We applied group independent component analysis (Group ICA) to construct the triple-network consisting of the saliency network (SN), the central executive network (CEN), and the default mode network (DMN) in 25 AD, 60 mild cognitive impairment (MCI) and 60 cognitively normal (CN) subjects. To explore the dynamic functional network connectivity (dFNC), we investigated dynamic time-varying triple-network interactions in subjects using Group ICA analysis based on k-means clustering (GDA-k-means). The mean of brain state-specific network interaction indices (meanNII) in the three groups (AD, MCI, CN) showed significant differences by ANOVA analysis. To verify the robustness of the findings, a support vector machine (SVM) was taken meanNII, gender and age as features to classify. This method obtained accuracy values of 95, 94, and 77% when classifying AD vs. CN, AD vs. MCI, and MCI vs. CN, respectively. In our work, the findings demonstrated that the dynamic characteristics of functional interactions of the triple-networks contributed to studying the underlying pathophysiology of AD. It provided strong evidence for dysregulation of brain dynamics of AD.Peer reviewedFinal Published versio
Cardiovascular magnetic resonance of quinticuspid aortic valve with aortic regurgitation and dilated ascending aorta
We report a rare case of a quinticuspid aortic valve associated with regurgitation and dilation of the ascending aorta, which was diagnosed and post-surgically followed up by cardiovascular magnetic resonance and dual source computed tomography
An Automatic Evaluation Framework for Multi-turn Medical Consultations Capabilities of Large Language Models
Large language models (LLMs) have achieved significant success in interacting
with human. However, recent studies have revealed that these models often
suffer from hallucinations, leading to overly confident but incorrect
judgments. This limits their application in the medical domain, where tasks
require the utmost accuracy. This paper introduces an automated evaluation
framework that assesses the practical capabilities of LLMs as virtual doctors
during multi-turn consultations. Consultation tasks are designed to require
LLMs to be aware of what they do not know, to inquire about missing medical
information from patients, and to ultimately make diagnoses. To evaluate the
performance of LLMs for these tasks, a benchmark is proposed by reformulating
medical multiple-choice questions from the United States Medical Licensing
Examinations (USMLE), and comprehensive evaluation metrics are developed and
evaluated on three constructed test sets. A medical consultation training set
is further constructed to improve the consultation ability of LLMs. The results
of the experiments show that fine-tuning with the training set can alleviate
hallucinations and improve LLMs' performance on the proposed benchmark.
Extensive experiments and ablation studies are conducted to validate the
effectiveness and robustness of the proposed framework.Comment: 10 pages, 9figure
AquaÂbis(triphenylÂphosphine-κP)copper(I) tetraÂfluoridoborate
In the title compound, [Cu(C18H15P)2(H2O)]BF4, the CuI atom is coordinated by two P atoms from triphenylÂphosphine ligands and one water molÂecule in a distorted trigonal geometry. In the BF4
− anion, three F atoms are disordered over two sites around the B—F bond, the site-occupancy ratio being 0.67 (6):0.33 (6). The Cu⋯F distance of 2.602 (5) Å between the Cu atom and the ordered F atom may suggest a weak but genuine interÂaction. O—H⋯F and weak C—H⋯F hydrogen bonding is present in the crystal structure
Electronic Structures of Graphene Layers on Metal Foil: Effect of Point Defects
Here we report a facile method to generate a high density of point defects in
graphene on metal foil and show how the point defects affect the electronic
structures of graphene layers. Our scanning tunneling microscopy (STM)
measurements, complemented by first principle calculations, reveal that the
point defects result in both the intervalley and intravalley scattering of
graphene. The Fermi velocity is reduced in the vicinity area of the defect due
to the enhanced scattering. Additionally, our analysis further points out that
periodic point defects can tailor the electronic properties of graphene by
introducing a significant bandgap, which opens an avenue towards all-graphene
electronics.Comment: 4 figure
Strain Induced One-Dimensional Landau-Level Quantization in Corrugated Graphene
Theoretical research has predicted that ripples of graphene generates
effective gauge field on its low energy electronic structure and could lead to
zero-energy flat bands, which are the analog of Landau levels in real magnetic
fields. Here we demonstrate, using a combination of scanning tunneling
microscopy and tight-binding approximation, that the zero-energy Landau levels
with vanishing Fermi velocities will form when the effective pseudomagnetic
flux per ripple is larger than the flux quantum. Our analysis indicates that
the effective gauge field of the ripples results in zero-energy flat bands in
one direction but not in another. The Fermi velocities in the perpendicular
direction of the ripples are not renormalized at all. The condition to generate
the ripples is also discussed according to classical thin-film elasticity
theory.Comment: 4 figures, Phys. Rev.
Enhanced Intervalley Scattering of Twisted Bilayer Graphene by Periodic AB Stacked Atoms
The electronic properties of twisted bilayer graphene on SiC substrate were
studied via combination of transport measurements and scanning tunneling
microscopy. We report the observation of enhanced intervalley scattering from
one Dirac cone to the other, which contributes to weak localization, of the
twisted bilayer graphene by increasing the interlayer coupling strength. Our
experiment and analysis demonstrate that the enhanced intervalley scattering is
closely related to the periodic AB stacked atoms (the A atom of layer 1 and the
B atom of layer 2 that have the same horizontal positions) that break the
sublattice degeneracy of graphene locally. We further show that these periodic
AB stacked atoms affect intervalley but not intravalley scattering. The result
reported here provides an effective way to atomically manipulate the
intervalley scattering of graphene.Comment: 4figure
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