652 research outputs found
Intervalley coupling by quantum dot confinement potentials in monolayer transition metal dichalcogenides
Monolayer transition metal dichalcogenides (TMDs) offer new opportunities for
realizing quantum dots (QDs) in the ultimate two-dimensional (2D) limit. Given
the rich control possibilities of electron valley pseudospin discovered in the
monolayers, this quantum degree of freedom can be a promising carrier of
information for potential quantum spintronics exploiting single electrons in
TMD QDs. An outstanding issue is to identify the degree of valley
hybridization, due to the QD confinement, which may significantly change the
valley physics in QDs from its form in the 2D bulk. Here we perform a
systematic study of the intervalley coupling by QD confinement potentials on
extended TMD monolayers. We find that the intervalley coupling in such geometry
is generically weak due to the vanishing amplitude of the electron wavefunction
at the QD boundary, and hence valley hybridization shall be well quenched by
the much stronger spin-valley coupling in monolayer TMDs and the QDs can well
inherit the valley physics of the 2D bulk. We also discover sensitive
dependence of intervalley coupling strength on the central position and the
lateral length scales of the confinement potentials, which may possibly allow
tuning of intervalley coupling by external controlsComment: 17 pages, 14 figure
The Quantitative Diagnosis Method of Rubbing Rotor System
The dynamics of the rubbing rotor system is analyzed by applying harmonic balance method. The relationship between harmonic components in the response of the rubbing rotor system and the dynamic stiffness matrix of the fault free rotor system is revealed, based on which a new model based method for rubbing identification is presented. By applying this method, the fault location and rubbing forces of the single rubbing rotor system can be identified by using vibration data of only two nodes, the rubbing locations and rubbing forces of the double rubbing rotor system can be identified by using vibration data of three nodes. The numerical simulations and experiments on the rotor test-rig are carried out to verify the efficiency of the present method
Active Learning for Graphs with Noisy Structures
Graph Neural Networks (GNNs) have seen significant success in tasks such as
node classification, largely contingent upon the availability of sufficient
labeled nodes. Yet, the excessive cost of labeling large-scale graphs led to a
focus on active learning on graphs, which aims for effective data selection to
maximize downstream model performance. Notably, most existing methods assume
reliable graph topology, while real-world scenarios often present noisy graphs.
Given this, designing a successful active learning framework for noisy graphs
is highly needed but challenging, as selecting data for labeling and obtaining
a clean graph are two tasks naturally interdependent: selecting high-quality
data requires clean graph structure while cleaning noisy graph structure
requires sufficient labeled data. Considering the complexity mentioned above,
we propose an active learning framework, GALClean, which has been specifically
designed to adopt an iterative approach for conducting both data selection and
graph purification simultaneously with best information learned from the prior
iteration. Importantly, we summarize GALClean as an instance of the
Expectation-Maximization algorithm, which provides a theoretical understanding
of its design and mechanisms. This theory naturally leads to an enhanced
version, GALClean+. Extensive experiments have demonstrated the effectiveness
and robustness of our proposed method across various types and levels of noisy
graphs
Research on Adaptive Neural Network Control System Based on Nonlinear U-Model with Time-Varying Delay
U-model can approximate a large class of smooth nonlinear time-varying delay system to any accuracy by using time-varying delay parameters polynomial. This paper proposes a new approach, namely, U-model approach, to solving the problems of analysis and synthesis for nonlinear systems. Based on the idea of discrete-time U-model with time-varying delay, the identification algorithm of adaptive neural network is given for the nonlinear model. Then, the controller is designed by using the Newton-Raphson formula and the stability analysis is given for the closed-loop nonlinear systems. Finally, illustrative examples are given to show the validity and applicability of the obtained results
Application of fuzzy random finite element method on rotor dynamics
Fuzzy and stochastic characteristics of parameters exist widely in rotating machinery. To research the parameters characteristics is of great significance in rotor dynamics. Dynamic characteristics of rotor system are analyzed taking into account uncertain properties of fuzzy and stochastic coexisting. Fuzzy variables are transformed into stochastic variables based on information entropy theory. The Neumann stochastic finite element method based on Neumann expansion combined with Newmark-β method is used in linear and nonlinear rotor system within the frame work of Monte Carlo simulation. Critical speed and dynamic response of fuzzy stochastic rotor systems are described by the proposed method. The results show that the Neumann stochastic finite element method has good applicability and efficiency in rotor dynamics
Comparison of Common Methods in Dynamic Response Predictions of Rotor Systems with Malfunctions
The efficiency and accuracy of common time and frequency domain methods that are used to simulate the response of a rotor system with malfunctions are compared and analyzed. The Newmark method and the incremental harmonic balance method are selected as typical representatives of time and frequency domain methods, respectively. To improve the simulation efficiency, the fixed interface component mode synthesis approach is combined with the Newmark method and the receptance approach is combined with the incremental harmonic balance method. Numerical simulations are performed for rotor systems with single and double frequency excitations. The inherent characteristic that determines the efficiency of the two methods is analyzed. The results of the analysis indicated that frequency domain methods are suitable single and double frequency excitation rotor systems, whereas time domain methods are more suitable for multifrequency excitation rotor systems
Electronic, optical and transport properties of van der Waals Transition-metal Dichalcogenides Heterostructures: A First-principle Study
Two-dimensional (2D) transition-metal dichalcogenide (TMD) MX (M = Mo, W;
X= S, Se, Te) possess unique properties and novel applications. In this work,
we perform first-principles calculations on the van der Waals (vdW) stacked
MX heterostructures to investigate their electronic, optical and transport
properties systematically. We perform the so-called Anderson's rule to classify
the heterostructures by providing the scheme of the construction of energy band
diagrams for the heterostructure consisting of two semiconductor materials. For
most of the MX heterostructures, the conduction band maximum (CBM) and
valence band minimum (VBM) reside in two separate semiconductors, forming type
II band structure, thus the electron-holes pairs are spatially separated. We
also find strong interlayer coupling at point after forming MX
heterostructures, even leading to the indirect band gap. While the band
structure near point remain as the independent monolayer. The carrier
mobilities of MX heterostructures depend on three decisive factors, elastic
modulus, effective mass and deformation potential constant, which are discussed
and contrasted with those of monolayer MX, respectively.Comment: 7 figure
Benign duodenocolic fistula: A case report and review of the literature
Duodenocolic fistula is a rare upper gastrointestinal fistula that can be benign or malignant. However, benign duodenocolic fistulas are particularly rare. Duodenocolic fistulas are often a complication of advanced colon cancer. The most common cause of benign fistulas is perforation of the duodenal ulcer. We report a case of a benign duodenocolic fistula in a patient who presented with abdominal pain, diarrhea, and weight loss. Gastroscopy and an upper gastrointestinal study confirmed the presence of the fistula. Surgery was performed, and the pathological examination demonstrated that the fistula originated from a duodenal ulcer
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