Combining Subgoal Graphs with Reinforcement Learning to Build a Rational Pathfinder

In this paper, we present a hierarchical path planning framework called SG-RL (subgoal graphs-reinforcement learning), to plan rational paths for agents maneuvering in continuous and uncertain environments. By "rational", we mean (1) efficient path planning to eliminate first-move lags; (2) collision-free and smooth for agents with kinematic constraints satisfied. SG-RL works in a two-level manner. At the first level, SG-RL uses a geometric path-planning method, i.e., Simple Subgoal Graphs (SSG), to efficiently find optimal abstract paths, also called subgoal sequences. At the second level, SG-RL uses an RL method, i.e., Least-Squares Policy Iteration (LSPI), to learn near-optimal motion-planning policies which can generate kinematically feasible and collision-free trajectories between adjacent subgoals. The first advantage of the proposed method is that SSG can solve the limitations of sparse reward and local minima trap for RL agents; thus, LSPI can be used to generate paths in complex environments. The second advantage is that, when the environment changes slightly (i.e., unexpected obstacles appearing), SG-RL does not need to reconstruct subgoal graphs and replan subgoal sequences using SSG, since LSPI can deal with uncertainties by exploiting its generalization ability to handle changes in environments. Simulation experiments in representative scenarios demonstrate that, compared with existing methods, SG-RL can work well on large-scale maps with relatively low action-switching frequencies and shorter path lengths, and SG-RL can deal with small changes in environments. We further demonstrate that the design of reward functions and the types of training environments are important factors for learning feasible policies.Comment: 20 page

Experimental behaviour of FRP-confined large-scale curvilinearized rectangular RC columns under axial compression

Existing research has shown that strengthening through fibre-reinforced polymer (FRP) confinement is highly effective for circular columns but much less so for sTuare and rectangular columns due to the flat sides and sharp corners in the latter. Rounding the corners in the latter columns can enhance the effectiveness of confinement, but its benefit is limited. To overcome this problem, an alternative strengthening techniTue has recently been proposed by some researchers, in which the flat sides of a sTuarerectangular section are modified into slightly curved sides before FRP confinement (referred to as section curvilinearization). The resulting columns, referred to as curvilinearized sTuare rectangular columns, are much more effectively confined by an FRP jacket than the original sTuarerectangular columns with only corner rounding, and the associated column size increase is limited. While this section curvilinearization techniTue is highly attractive, there has been only very limited research on the behaviour of FRP-confined curvilinearized sTuare rectangular columns. In particular, all the existing experimental work has been limited to small-scale sTuare columns (with section widths being around or below 1 mm) under axial compression. Against the above background, a large experimental programme has been under way at The Hong Kong Polytechnic University to study the behaviour of large-scale curvilinearized RC columns under both concentric and eccentric compression. Both sTuare and rectangular columns have been considered in the experimental programme. This paper presents a systematic experimental study on the behaviour of FRP-confined curvilinearized rectangular RC columns under axial compression to study the effects of the following parameters: rise-to-span ratio of the edge profile, sectional aspect ratio and corner radius. In addition to the presentation of experimental results, two existing stress-strain models for FRP-confined concrete in these columns are assessed to reveal their limitations

Column-Spatial Correction Network for Remote Sensing Image Destriping

The stripe noise in the multispectral remote sensing images, possibly resulting from the instrument instability, slit contamination, and light interference, significantly degrades the imaging quality and impairs high-level visual tasks. The local consistency of homogeneous region in striped images is damaged because of the different gains and offsets of adjacent sensors regarding the same ground object, which leads to the structural characteristics of stripe noise. This can be characterized by the increased differences between columns in the remote sensing image. Therefore, the destriping can be viewed as a process of improving the local consistency of homogeneous region and the global uniformity of whole image. In recent years, convolutional neural network (CNN)-based models have been introduced to destriping tasks, and have achieved advanced results, relying on their powerful representation ability. Therefore, to effectively leverage both CNNs and the structural characteristics of stripe noise, we propose a multi-scaled column-spatial correction network (CSCNet) for remote sensing image destriping, in which the local structural characteristic of stripe noise and the global contextual information of the image are both explored at multiple feature scales. More specifically, the column-based correction module (CCM) and spatial-based correction module (SCM) were designed to improve the local consistency and global uniformity from the perspectives of column correction and full image correction, respectively. Moreover, a feature fusion module based on the channel attention mechanism was created to obtain discriminative features derived from different modules and scales. We compared the proposed model against both traditional and deep learning methods on simulated and real remote sensing images. The promising results indicate that CSCNet effectively removes image stripes and outperforms state-of-the-art methods in terms of qualitative and quantitative assessments

Berry-Curvature Engineering for Nonreciprocal Directional Dichroism in Two-Dimensional Antiferromagnets

In two-dimensional antiferromagnets, we identify the mixed Berry curvature as the geometrical origin of the nonreciprocal directional dichroism (NDD), which refers to the difference in light absorption with the propagation direction flipped. Such a Berry curvature is strongly tied to the uniaxial strain in accordance with the symmetry constraint, leading to a highly tunable NDD, whose sign and magnitude can be manipulated via the strain direction. As a concrete example, we demonstrate such a phenomenon in a lattice model of MnBi2Te4. The coupling between the mixed Berry curvature and strain also suggests the magnetic quadrupole of the Bloch wave packet as the macroscopic order parameter probed by the NDD in two dimensions, distinct from the multiferroic order P times M or the spin toroidal and quadrupole order within a unit cell in previous studies. Our work paves the way of the Berry-curvature engineering for optical nonreciprocity in two-dimensional antiferromagnets

Chiral-Flux-Phase-Based Topological Superconductivity in Kagome Systems with Mixed Edge Chiralities

Recent studies have attracted intense attention on the quasi-2D kagome superconductors $A\text{V}_3\text{Sb}_5$ ($A =$ K, Rb, and Cs) where the unexpected chiral flux phase (CFP) associates with the spontaneous time-reversal symmetry breaking in charge density wave (CDW) states. Here, commencing from the 2-by-2 CDW phases, we bridge the gap between topological superconductivity (TSC) and time-reversal asymmetric CFP in kagome systems. Several chiral TSC states featuring distinct Chern numbers emerge for an s-wave or a d-wave superconducting pairing symmetry. Importantly, these CFP-based TSC phases possess unique gapless edge modes with mixed chiralities (i.e., both positive and negative chiralities), but with the net chiralities consistent with the Bogoliubov-de Gennes Chern numbers. We further study the transport properties of a two-terminal junction, using Chern insulator or normal metal leads via atomic Green's function method with Landauer-B\"uttiker formalism. In both cases, the normal electron tunneling and the crossed Andreev reflection oscillate as the chemical potential changes, but together contribute to plateau transmissions (1 and 3/2, respectively). These behaviors can be regarded as the signature of a topological superconductor hosting edge states with mixed chiralities.Comment: 6 pages, 4 figure