146 research outputs found
Orientation-Dependent Atomic-Scale Mechanism of - Thin Film Epitaxial Growth
- has gained intensive interests of
research and application as an ultrawide bandgap semiconductor. Epitaxial
growth technique of the - thin film
possesses a fundamental and vital role in the
-based device fabrication. In this work,
epitaxial growth mechanisms of - with
four low Miller-index facets, namely (100), (010), (001), and
(01), are systematically explored using large-scale
machine-learning molecular dynamics simulations at the atomic scale. The
simulations reveal that the migration of the face-centered cubic stacking O
sublattice plays a predominant role in rationalizing the different growth
mechanisms between (100)/(010)/(001) and (01) orientations. The
resultant complex combinations of the stacking faults and twin boundaries are
carefully identified, and shows a good agreement with the experimental
observation and ab initio calculation. Our results provide useful insights into
the gas-phase epitaxial growth of the -
thin films and suggest possible ways to tailor its properties for specific
applications.Comment: 6 pages, 5 figures, under peer revie
RESURF GaO-on-SiC Field Effect Transistors for Enhanced Breakdown Voltage
Heterosubstrates have been extensively studied as a method to improve the
heat dissipation of GaO devices. In this simulation work, we
propose a novel role for -type available heterosubstrates, as a component of
a reduced surface field (RESURF) structure in GaO lateral
field-effect transistors (FETs). The RESURF structure can eliminate the
electric field crowding and contribute to higher breakdown voltage. Using SiC
as an example, the designing strategy for doping concentration and dimensions
of the -type region is systematically studied using TCAD modeling. To mimic
realistic devices, the impacts of interface charge and binding interlayer at
the GaO/SiC interface are also explored. Additionally, the
feasibility of the RESURF structure for high-frequency switching operation is
supported by the short time constant (0.5 ns) of charging/discharging the
-SiC depletion region. This study demonstrates the great potential of
utilizing the electrical properties of heat-dissipating heterosubstrates to
achieve a uniform electric field distribution in GaO FETs.Comment: 6 pages, 7 figures, under revie
Causal conditional hidden Markov model for multimodal traffic prediction
Multimodal traffic flow can reflect the health of the transportation system,
and its prediction is crucial to urban traffic management. Recent works
overemphasize spatio-temporal correlations of traffic flow, ignoring the
physical concepts that lead to the generation of observations and their causal
relationship. Spatio-temporal correlations are considered unstable under the
influence of different conditions, and spurious correlations may exist in
observations. In this paper, we analyze the physical concepts affecting the
generation of multimode traffic flow from the perspective of the observation
generation principle and propose a Causal Conditional Hidden Markov Model
(CCHMM) to predict multimodal traffic flow. In the latent variables inference
stage, a posterior network disentangles the causal representations of the
concepts of interest from conditional information and observations, and a
causal propagation module mines their causal relationship. In the data
generation stage, a prior network samples the causal latent variables from the
prior distribution and feeds them into the generator to generate multimodal
traffic flow. We use a mutually supervised training method for the prior and
posterior to enhance the identifiability of the model. Experiments on
real-world datasets show that CCHMM can effectively disentangle causal
representations of concepts of interest and identify causality, and accurately
predict multimodal traffic flow.Comment: 8 pages, 5 figure
The Research on Exogenous Problems of Farmers’ Piritual and Cultural Education in China
The author studied and analyzed the exogenous problems of the farmers’ spiritual and cultural education, and found out: In today’s China, the exogenous problems of the farmers’ spiritual and cultural education mainly reflected in the separation of spiritual and cultural education is from social environment, political system, economic development, and cultural concepts etc. Then the author put forward to the countermeasures and suggestions aimed at optimizing the allocation of famers’ spiritual and cultural educations resources, environment and evaluation system construction and so on
Changes in element accumulation, phenolic metabolism, and antioxidative enzyme activities in the red-skin roots of Panax ginseng
AbstractBackgroundRed-skin root disease has seriously decreased the quality and production of Panax ginseng (ginseng).MethodsTo explore the disease's origin, comparative analysis was performed in different parts of the plant, particularly the epidermis, cortex, and/or fibrous roots of 5-yr-old healthy and diseased red-skin ginseng. The inorganic element composition, phenolic compound concentration, reactive oxidation system, antioxidant concentrations such as ascorbate and glutathione, activities of enzymes related to phenolic metabolism and oxidation, and antioxidative system particularly the ascorbate–glutathione cycle were examined using conventional methods.ResultsAluminum (Al), iron (Fe), magnesium, and phosphorus were increased, whereas manganese was unchanged and calcium was decreased in the epidermis and fibrous root of red-skin ginseng, which also contained higher levels of phenolic compounds, higher activities of the phenolic compound-synthesizing enzyme phenylalanine ammonia-lyase and the phenolic compound oxidation-related enzymes guaiacol peroxidase and polyphenoloxidase. As the substrate of guaiacol peroxidase, higher levels of H2O2 and correspondingly higher activities of superoxide dismutase and catalase were found in red-skin ginseng. Increased levels of ascorbate and glutathione; increased activities of l-galactose 1-dehydrogenase, ascorbate peroxidase, ascorbic acid oxidase, and glutathione reductase; and lower activities of dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione peroxidase were found in red-skin ginseng. Glutathione-S-transferase activity remained constant.ConclusionHence, higher element accumulation, particularly Al and Fe, activated multiple enzymes related to accumulation of phenolic compounds and their oxidation. This might contribute to red-skin symptoms in ginseng. It is proposed that antioxidant and antioxidative enzymes, especially those involved in ascorbate–glutathione cycles, are activated to protect against phenolic compound oxidation
Preparation and imaging of intravascular high-frequency transducer
Intravascular ultrasound (IVUS) imaging is by far the most favorable imaging modality for coronary artery evaluation. IVUS transducer design and fabrication, a key technology for intravascular ultrasound imaging, has a significant impact on the performance of the imaging results. Herein, a 35-MHz side-looking IVUS transducer probe was developed. With a small aperture of 0.40 mm × 0.40 mm, the transducer exhibited a very wide -6 dB bandwidth of 85% and a very low insertion loss of -12 dB. Further, the in vitro IVUS imaging of a porcine coronary artery was performed to clearly display the vessel wall structure while the corresponding color-coded graph was constructed successfully to distinguish necrotic core and fibrous plaque via image processing. The results demonstrated that the imaging performance of the optimized design transducer performs favorably
Tetragonal Mexican-Hat Dispersion and Switchable Half-Metal State with Multiple Anisotropic Weyl Fermions in Penta-Graphene
In past decades, the ever-expanding library of 2D carbon allotropes has
yielded a broad range of exotic properties for the future carbon-based
electronics. However, the known allotropes are all intrinsic nonmagnetic due to
the paired valence electrons configuration. Based on the reported 2D carbon
structure database and first-principles calculations, herein we demonstrate
that inherent ferromagnetism can be obtained in the prominent allotrope,
penta-graphene, which has an unique Mexican-hat valence band edge, giving rise
to van Hove singularities and electronic instability. Induced by modest
hole-doping, being achievable in electrolyte gate, the semiconducting
pentagraphene can transform into different ferromagnetic half-metals with room
temperature stability and switchable spin directions. In particular, multiple
anisotropic Weyl states, including type-I and type-II Weyl cones and hybrid
quasi Weyl nodal loop, can be found in a sizable energy window of spin-down
half-metal under proper strains. These findings not only identify a promising
carbon allotrope to obtain the inherent magnetism for carbon-based spintronic
devices, but highlight the possibility to realize different Weyl states by
combining the electronic and mechanical means as well
TeacherLM: Teaching to Fish Rather Than Giving the Fish, Language Modeling Likewise
Large Language Models (LLMs) exhibit impressive reasoning and data
augmentation capabilities in various NLP tasks. However, what about small
models? In this work, we propose TeacherLM-7.1B, capable of annotating relevant
fundamentals, chain of thought, and common mistakes for most NLP samples, which
makes annotation more than just an answer, thus allowing other models to learn
"why" instead of just "what". The TeacherLM-7.1B model achieved a zero-shot
score of 52.3 on MMLU, surpassing most models with over 100B parameters. Even
more remarkable is its data augmentation ability. Based on TeacherLM-7.1B, we
augmented 58 NLP datasets and taught various student models with different
parameters from OPT and BLOOM series in a multi-task setting. The experimental
results indicate that the data augmentation provided by TeacherLM has brought
significant benefits. We will release the TeacherLM series of models and
augmented datasets as open-source.Comment: 5 figures, 15 page
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