We model the newly synthesized magic-angle-twisted bilayer graphene superconductor with two p_{x,y}-like Wannier orbitals on the superstructure honeycomb lattice, where the hopping integrals are ...constructed via the Slater-Koster formulism by symmetry analysis. The characteristics exhibited in this simple model are well consistent with both the rigorous calculations and experiment observations. A van Hove singularity and Fermi-surface (FS) nesting are found in the doping levels relevant to the correlated insulator and unconventional superconductivity revealed experimentally, based on which we identify the two phases as weak-coupling FS instabilities. Then, with repulsive Hubbard interactions turned on, we performed random-phase-approximation based calculations to identify the electron instabilities. As a result, we find chiral d+id topological superconductivity bordering the correlated insulating state near half-filling, identified as noncoplanar chiral spin-density wave ordered state, featuring the quantum anomalous Hall effect. The phase diagram obtained in our approach is qualitatively consistent with experiments.
In this brief, an adaptive robust finite-time tracking control (ARFTTC) scheme for trajectory tracking of a fully actuated marine surface vehicle with unknown disturbances is proposed. A new ...finite-time disturbance observer is incorporated into the proposed finite-time tracking control (FTTC) structure that facilitates faster convergence and better robustness to disturbances. Hence, in the presence of unknown disturbances, the ARFTTC can cause tracking error to converge to zero in a finite time. Simulation studies and comprehensive comparisons with conventional backstepping technique demonstrate remarkable performance and superiority of the ARFTTC in terms of both tracking accuracy and robustness.
Single noble metal atoms and ultrafine metal clusters catalysts tend to sinter into aggregated particles at elevated temperatures, driven by the decrease of metal surface free energy. Herein, we ...report an unexpected phenomenon that noble metal nanoparticles (Pd, Pt, Au-NPs) can be transformed to thermally stable single atoms (Pd, Pt, Au-SAs) above 900 °C in an inert atmosphere. The atomic dispersion of metal single atoms was confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption fine structures. The dynamic process was recorded by in situ environmental transmission electron microscopy, which showed competing sintering and atomization processes during NP-to-SA conversion. Further, density functional theory calculations revealed that high-temperature NP-to-SA conversion was driven by the formation of the more thermodynamically stable Pd-N
structure when mobile Pd atoms were captured on the defects of nitrogen-doped carbon. The thermally stable single atoms (Pd-SAs) exhibited even better activity and selectivity than nanoparticles (Pd-NPs) for semi-hydrogenation of acetylene.
Recent deep learning based approaches have achieved great success on handwriting recognition. Chinese characters are among the most widely adopted writing systems in the world. Previous research has ...mainly focused on recognizing handwritten Chinese characters. However, recognition is only one aspect for understanding a language, another challenging and interesting task is to teach a machine to automatically write (pictographic) Chinese characters. In this paper, we propose a framework by using the recurrent neural network (RNN) as both a discriminative model for recognizing Chinese characters and a generative model for drawing (generating) Chinese characters. To recognize Chinese characters, previous methods usually adopt the convolutional neural network (CNN) models which require transforming the online handwriting trajectory into image-like representations. Instead, our RNN based approach is an end-to-end system which directly deals with the sequential structure and does not require any domain-specific knowledge. With the RNN system (combining an LSTM and GRU), state-of-the-art performance can be achieved on the ICDAR-2013 competition database. Furthermore, under the RNN framework, a conditional generative model with character embedding is proposed for automatically drawing recognizable Chinese characters. The generated characters (in vector format) are human-readable and also can be recognized by the discriminative RNN model with high accuracy. Experimental results verify the effectiveness of using RNNs as both generative and discriminative models for the tasks of drawing and recognizing Chinese characters.
This paper introduces a video representation based on dense trajectories and motion boundary descriptors. Trajectories capture the local motion information of the video. A dense representation ...guarantees a good coverage of foreground motion as well as of the surrounding context. A state-of-the-art optical flow algorithm enables a robust and efficient extraction of dense trajectories. As descriptors we extract features aligned with the trajectories to characterize shape (point coordinates), appearance (histograms of oriented gradients) and motion (histograms of optical flow). Additionally, we introduce a descriptor based on motion boundary histograms (MBH) which rely on differential optical flow. The MBH descriptor shows to consistently outperform other state-of-the-art descriptors, in particular on real-world videos that contain a significant amount of camera motion. We evaluate our video representation in the context of action classification on nine datasets, namely KTH, YouTube, Hollywood2, UCF sports, IXMAS, UIUC, Olympic Sports, UCF50 and HMDB51. On all datasets our approach outperforms current state-of-the-art results.
Gold nanoechinus can sensitize the formation of singlet oxygen in the first and the second near‐infra red (NIR) biological windows and exert in vivo dual modal photodynamic and photothermal ...therapeutic effects (PDT and PTT) to destruct the tumors completely. This is the first literature example of the destruction of tumors in NIR window II induced by dual modal nanomaterial‐mediated photodynamic and photothermal therapy (NmPDT & NmPTT).
Three new zinc(II) and one vanadium(V) complexes, Zn2Cl2L2 (1), Zn2I2L2 (2), ZnCl2(HL) (3), and V2O2(μ-O)2L2 (4), where L is 5-bromo-2-((2-(methylamino)ethylimino)methyl)phenolate, have been ...synthesized and characterized by elemental analyses, IR and UV-Vis spectra, as well as molar conductivity. Structures of the complexes were confirmed by single crystal X-ray diffraction. Complexes 1 and 2 are isostructural dinuclear zinc compounds, with the Zn atoms in square pyramidal coordination. The Zn atoms in the mononuclear complex 3 are in tetrahedral coordination. Complex 4 is a dinuclear vanadium(V) compound, with the V atoms in octahedral coordination. The complexes were assayed for antibacterial activities by MTT method.
Water transport rate in network membranes is inversely correlated to thickness, thus superior permeance is achievable with ultrathin membranes prepared by complicated methods circumventing nanofilm ...weakness and defects. Conferring ultrahigh permeance to easily prepared thicker membranes remains challenging. Here, a tetrakis(hydroxymethyl) phosphonium chloride (THPC) monomer is discovered that enables straightforward modification of polyamide composite membranes. Water permeance of the modified membrane is ≈6 times improved, give rising to permeability (permeance × thickness) one magnitude higher than state‐of‐the‐art polymer nanofiltration membranes. Meanwhile, the membrane exhibits good rejection (RNa2SO4 = 98%) and antibacterial properties under crossflow conditions. THPC modification not only improves membrane hydrophilicity, but also creates additional angstrom‐scale channels in polyamide membranes for unimpeded transport of water. This unique mechanism provides a paradigm shift in facile preparation of ultrapermeable membranes with unreduced thickness for clean water and desalination.
Facile modification of polyamide composite membranes by an inexpensive phosphonium monomer featuring tetrahedral geometry is found to create additional water transport channels, improving the water purification performance without reducing film thickness. Compared with cutting‐edge ultrathin membranes, the modified membrane highlights good rejection, antibacterial properties, superior water permeability, and facile preparation.
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