BLADE: Box-Level Supervised Amodal Segmentation through Directed Expansion

Perceiving the complete shape of occluded objects is essential for human and machine intelligence. While the amodal segmentation task is to predict the complete mask of partially occluded objects, it is time-consuming and labor-intensive to annotate the pixel-level ground truth amodal masks. Box-level supervised amodal segmentation addresses this challenge by relying solely on ground truth bounding boxes and instance classes as supervision, thereby alleviating the need for exhaustive pixel-level annotations. Nevertheless, current box-level methodologies encounter limitations in generating low-resolution masks and imprecise boundaries, failing to meet the demands of practical real-world applications. We present a novel solution to tackle this problem by introducing a directed expansion approach from visible masks to corresponding amodal masks. Our approach involves a hybrid end-to-end network based on the overlapping region - the area where different instances intersect. Diverse segmentation strategies are applied for overlapping regions and non-overlapping regions according to distinct characteristics. To guide the expansion of visible masks, we introduce an elaborately-designed connectivity loss for overlapping regions, which leverages correlations with visible masks and facilitates accurate amodal segmentation. Experiments are conducted on several challenging datasets and the results show that our proposed method can outperform existing state-of-the-art methods with large margins.Comment: Accepted to AAAI 202

Dynamical magnetoelectric coupling in axion insulator thin films

Axion insulator is an exotic magnetic topological insulator with zero Chern number but a nonzero quantized Chern-Simons magnetoelectric coupling. A conclusive experimental evidence for axion insulators is still lacking due to the small signal of topological magnetoelectric effect (TME). Here we show that the dynamical magnetoelectric coupling can be induced by the \emph{out-of-plane} surface magnetization dynamics in axion insulator thin films, which further generates a polarization current in the presence of an external magnetic field in the same direction. Such a current is finite in the bulk and increases as the film thickness $d$ decreases, in opposite to TME current which decreases as $d$ decreases. Remarkably, the current in thin films at magnetic resonance is at least ten times larger than that of TME, and thus may serve as a smoking gun signature for axion insulators.Comment: 5 pages, 4 figure

Dissipative Edge Transport in Disordered Axion Insulator Films

We investigate the role of disorder in the edge transport of axion insulator films. We predict by first-principles calculations that even-number-layer MnBi$_2$Te$_4$ have gapped helical edge states. The random potential will dramatically modify the edge spectral function to become gapless. However, such gapless helical state here is fundamentally different from that in quantum spin Hall insulator or topological Anderson insulator. We further study the edge transport in this system by Landauer-B\"{u}ttiker formalism, and find such gapless edge state is dissipative and not immune to backscattering, which would explain the dissipative nonlocal transport in the axion insulator state observed in six septuple layer MnBi$_2$Te$_4$ experimentally. Several transport experiments are proposed to verify our theory on the dissipative helical edge channels. In particular, the longitudinal resistance can be greatly reduced by adding an extra floating probe even if it is not used. These results will facilitate the observsation of long-sought topological magnetoelectric effect in axion insulators.Comment: 7pages,4 figure

Giant anisotropic band flattening in twisted Γ\Gamma valley semiconductor bilayers

We propose a theory of anisotropic band flattening in moir\'e systems at the $\Gamma$ valley. We find that in twisted anisotropic two-dimensional crystals with a rectangular unit cell of $C_{2z}$ or mirror symmetries, a larger effective mass anisotropy $\eta=m_y/m_x$ has a stronger tendency to be further enhanced compared to that of monolayer, which leads to correlated physics in one dimension effectively. We predict twisted bilayer black phosphorus (tBBP) has giant anisotropic flattened moir\'e bands ($\eta\sim10^4$) from ab initio calculations and continuum model, where the low energy physics is described by the weakly coupled array of one-dimensional wires. We further calculate the phase diagram based on sliding Luttinger liquid by including the screened Coulomb interactions in tBBP, and find a large parameter space may host the non-Fermi liquid phase. We thus establish tBBP as a promising and experimentally accessible platform for exploring correlated physics in low dimensions.Comment: 5 pages, 4 figure

Monolayer V2MX4: A new family of quantum anomalous Hall insulators

We theoretically propose that the van der Waals layered ternary transition metal chalcogenide V$_2 MX_4$ ($M=$ W, Mo; $X=$ S, Se) is a new family of quantum anomalous Hall insulators with sizable bulk gap and Chern number $\mathcal{C}=-1$. The large topological gap originates from the \emph{deep} band inversion between spin up bands contributed by $d_{xz},d_{yz}$ orbitals of V and spin down band from $d_{z^2}$ orbital of $M$ at Fermi level. Remarkably, the Curie temperature of monolayer V$_2 MX_4$ is predicted to be much higher than that of monolayer MnBi$_2$Te$_4$. Furthermore, the thickness dependence of the Chern number for few multilayers shows interesting oscillating behavior. The general physics from the $d$-orbitals here applies to a large class of ternary transition metal chalcogenide such as Ti$_2$W$X_4$ with the space group $P$-$42m$. These interesting predictions, if realized experimentally, could greatly promote the research and application of topological quantum physics.Comment: 7 pages, 4 figure

Modeling of Particle Behavior in a Wurster Fluidized Bed: Coupling CFD-DEM with Monte Carlo

[EN] CFD-DEM approach is applied to investigate circulation motion of particles in a mono-disperse system under both dry and wetting conditions. Good agreement between simulation results and measurement data is observed, in terms of cycle time and residence time in dry condition. The deposition of droplets on the particle surface is modeled by a Monte Carlo approach. The influence of cohesion forces on the macroscopic particle circulation is discussed. In addition, information about coating coverage, the layer thickness and particle size distribution can be predicted by this integrating approach.The authors gratefully acknowledge the funding of this work by the German Federal Ministry of Science and Education (BMBF) as a part of the InnoProfileTransfer project NaWiTec (03IPT701X).Jiang, Z.; Rieck, C.; Bück, A.; Tsotsas, E. (2018). Modeling of Particle Behavior in a Wurster Fluidized Bed: Coupling CFD-DEM with Monte Carlo. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 205-212. https://doi.org/10.4995/IDS2018.2018.7239OCS20521

Investigation of 3D particle flow in a flighted rotating drum

[EN] o validate the particle motion in flighted rotating drum (FRD), a laboratory FRD was built and operated at 15% filling degree and 10 rpm rotation speed using plastic balls as bed material. The particle tracking velocimetry (PTV) and magnetic particle tracking (MPT) techniques were applied to investigate the particle flow behavior. The 3D particle flow was modeled by Discrete Element Method (DEM) with LIGGGHTS. The height of the barycenter of all overall particles and particle instantaneous velocity were calculated from PTV and DEM data. The 3D time-averaged particle velocity distributions obtained from MPT experiment and DEM simulation were compared.Zhang, L.; Weigler, F.; Jiang, Z.; Idakiev, V.; Mörl, L.; Mellmann, J.; Tsotsas, E. (2018). Investigation of 3D particle flow in a flighted rotating drum. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 253-260. https://doi.org/10.4995/IDS2018.2018.7389OCS25326