4,911 research outputs found
The origin of p-type conduction in (P, N) co-doped ZnO
P mono-doped and (P, N) co-doped ZnO are investigated by the first-principles
calculations. It is found that substitutive P defect forms a deep acceptor
level at O site (PO) and it behaves as a donor at Zn site (PZn), while
interstitial P (Pi) is amphoteric. Under equilibrium conditions, these defects
contribute little to the p-type conductivity of ZnO samples since the formation
energy of PZn is much lower than that of Pi or PO when EF is below mid-gap (a
prerequisite p-type condition). Zinc vacancies (VZn) and PZn-2VZn complex are
demonstrated to be shallow acceptors with ionization energies around 100 meV,
but they are easily compensated by PZn defect. Fortunately, PZn-4NO complexes
may have lower formation energy than that of PZn under Zn rich condition by
proper choices of P and N sources. In addition, the neutral PZn-3NO passive
defects may form an impurity band right above the valence band maximum of ZnO
as in earlier reported (Ga,N) or (Zr,N) doped ZnO. This significantly reduces
the acceptor level of PZn-4NO complexes, and helps improving the p-type
conductivity in ZnO.Comment: 25 pages, 7 figure
Dynamics of delay induced composite multi-scroll attractor and its application in encryption
This work was supported in part by NSFC (60804040, 61172070), Key Program of Nature Science Foundation of Shaanxi Province (2016ZDJC-01), Innovative Research Team of Shaanxi Province(2013KCT-04), Fok Ying Tong Education Foundation Young Teacher Foundation(111065), Chao Bai was supported by Excellent Ph.D. research fund (310-252071603) at XAUT.Peer reviewedPostprin
MSAT: Matrix stability analysis tool for shock-capturing schemes
The simulation of supersonic or hypersonic flows often suffers from numerical
shock instabilities if the flow field contains strong shocks, limiting the
further application of shock-capturing schemes. In this paper, we develop the
unified matrix stability analysis method for schemes with three-point stencils
and present MSAT, an open-source tool to quantitatively analyze the shock
instability problem. Based on the finite-volume approach on the structured
grid, MSAT can be employed to investigate the mechanism of the shock
instability problem, evaluate the robustness of numerical schemes, and then
help to develop robust schemes. Also, MSAT has the ability to analyze the
practical simulation of supersonic or hypersonic flows, evaluate whether it
will suffer from shock instabilities, and then assist in selecting appropriate
numerical schemes accordingly. As a result, MSAT is a helpful tool that can
investigate the shock instability problem and help to cure it.Comment: 18 pages, 6 figure
New Fast Fall Detection Method Based on Spatio-Temporal Context Tracking of Head by Using Depth Images
© 2015 by the authors; licensee MDPI, Basel, Switzerland. In order to deal with the problem of projection occurring in fall detection with two-dimensional (2D) grey or color images, this paper proposed a robust fall detection method based on spatio-temporal context tracking over three-dimensional (3D) depth images that are captured by the Kinect sensor. In the pre-processing procedure, the parameters of the Single-Gauss-Model (SGM) are estimated and the coefficients of the floor plane equation are extracted from the background images. Once human subject appears in the scene, the silhouette is extracted by SGM and the foreground coefficient of ellipses is used to determine the head position. The dense spatio-temporal context (STC) algorithm is then applied to track the head position and the distance from the head to floor plane is calculated in every following frame of the depth image. When the distance is lower than an adaptive threshold, the centroid height of the human will be used as the second judgment criteria to decide whether a fall incident happened. Lastly, four groups of experiments with different falling directions are performed. Experimental results show that the proposed method can detect fall incidents that occurred in different orientations, and they only need a low computation complexity
3D Stretchable Arch Ribbon Array Fabricated via Grayscale Lithography.
Microstructures with flexible and stretchable properties display tremendous potential applications including integrated systems, wearable devices and bio-sensor electronics. Hence, it is essential to develop an effective method for fabricating curvilinear and flexural microstructures. Despite significant advances in 2D stretchable inorganic structures, large scale fabrication of unique 3D microstructures at a low cost remains challenging. Here, we demonstrate that the 3D microstructures can be achieved by grayscale lithography to produce a curved photoresist (PR) template, where the PR acts as sacrificial layer to form wavelike arched structures. Using plasma-enhanced chemical vapor deposition (PECVD) process at low temperature, the curved PR topography can be transferred to the silicon dioxide layer. Subsequently, plasma etching can be used to fabricate the arched stripe arrays. The wavelike silicon dioxide arch microstructure exhibits Young modulus and fracture strength of 52 GPa and 300 MPa, respectively. The model of stress distribution inside the microstructure was also established, which compares well with the experimental results. This approach of fabricating a wavelike arch structure may become a promising route to produce a variety of stretchable sensors, actuators and circuits, thus providing unique opportunities for emerging classes of robust 3D integrated systems
Learning World Models with Identifiable Factorization
Extracting a stable and compact representation of the environment is crucial
for efficient reinforcement learning in high-dimensional, noisy, and
non-stationary environments. Different categories of information coexist in
such environments -- how to effectively extract and disentangle these
information remains a challenging problem. In this paper, we propose IFactor, a
general framework to model four distinct categories of latent state variables
that capture various aspects of information within the RL system, based on
their interactions with actions and rewards. Our analysis establishes
block-wise identifiability of these latent variables, which not only provides a
stable and compact representation but also discloses that all reward-relevant
factors are significant for policy learning. We further present a practical
approach to learning the world model with identifiable blocks, ensuring the
removal of redundants but retaining minimal and sufficient information for
policy optimization. Experiments in synthetic worlds demonstrate that our
method accurately identifies the ground-truth latent variables, substantiating
our theoretical findings. Moreover, experiments in variants of the DeepMind
Control Suite and RoboDesk showcase the superior performance of our approach
over baselines
Predicting mutational effects on protein-protein binding via a side-chain diffusion probabilistic model
Many crucial biological processes rely on networks of protein-protein
interactions. Predicting the effect of amino acid mutations on protein-protein
binding is vital in protein engineering and therapeutic discovery. However, the
scarcity of annotated experimental data on binding energy poses a significant
challenge for developing computational approaches, particularly deep
learning-based methods. In this work, we propose SidechainDiff, a
representation learning-based approach that leverages unlabelled experimental
protein structures. SidechainDiff utilizes a Riemannian diffusion model to
learn the generative process of side-chain conformations and can also give the
structural context representations of mutations on the protein-protein
interface. Leveraging the learned representations, we achieve state-of-the-art
performance in predicting the mutational effects on protein-protein binding.
Furthermore, SidechainDiff is the first diffusion-based generative model for
side-chains, distinguishing it from prior efforts that have predominantly
focused on generating protein backbone structures
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