The edge engineering of topological Bi(111) bilayer

A topological insulator is a novel quantum state, characterized by symmetry-protected non-trivial edge/surface states. Our first-principle simulations show the significant effects of the chemical decoration on edge states of topological Bi(111) bilayer nanoribbon, which remove the trivial edge state and recover the Dirac linear dispersion of topological edge state. By comparing the edge states with and without chemical decoration, the Bi(111) bilayer nanoribbon offers a simple system for assessing conductance fluctuation of edge states. The chemical decoration can also modify the penetration depth and the spin texture of edge states. A low-energy effective model is proposed to explain the distinctive spin texture of Bi(111) bilayer nanoribbon, which breaks the spin-momentum orthogonality along the armchair edge.Comment: 5 pages, 5 figure

A hierarchical control framework for autonomous decision-making systems: Integrating HMDP and MPC

This paper proposes a comprehensive hierarchical control framework for autonomous decision-making arising in robotics and autonomous systems. In a typical hierarchical control architecture, high-level decision making is often characterised by discrete state and decision/control sets. However, a rational decision is usually affected by not only the discrete states of the autonomous system, but also the underlying continuous dynamics even the evolution of its operational environment. This paper proposes a holistic and comprehensive design process and framework for this type of challenging problems, from new modelling and design problem formulation to control design and stability analysis. It addresses the intricate interplay between traditional continuous systems dynamics utilized at the low levels for control design and discrete Markov decision processes (MDP) for facilitating high-level decision making. We model the decision making system in complex environments as a hybrid system consisting of a controlled MDP and autonomous (i.e. uncontrolled) continuous dynamics. Consequently, the new formulation is called as hybrid Markov decision process (HMDP). The design problem is formulated with a focus on ensuring both safety and optimality while taking into account the influence of both the discrete and continuous state variables of different levels. With the help of the model predictive control (MPC) concept, a decision maker design scheme is proposed for the proposed hybrid decision making model. By carefully designing key ingredients involved in this scheme, it is shown that the recursive feasibility and stability of the proposed autonomous decision making scheme are guaranteed. The proposed framework is applied to develop an autonomous lane changing system for intelligent vehicles.Comment: 11 pages, 14 figures, submitted to Automatic

Ixeridium sagittarioides (Asteraceae-Cichorieae) revisited: range extension and molecular evidence for its systematic position in the Lactuca alliance

Our first record of the rare and scatteredly distributed Ixeridium sagittarioides for Guizhou, China, triggered a study to assess its systematic position. The species was placed in four different genera in the course of its taxonomic history and was recently treated with doubts as a member of Ixeridium in the Flora of China. Comparative morphological investigation and phylogenetic analyses based on the nuclear ribosomal DNA internal transcribed spacer (nrITS) and five non-coding plastid DNA regions (petD region, psbA-trnH, trnL-trnF, rpl32-trnL (UAG) and 5´rps16-trnQ (UUG) spacers) provided evidence that the species is not a member of Ixeridium and the Crepidinae but has evolved by ancient hybridisation of members of the Lactuca alliance (Lactucinae). It is reinstated as Lactuca sagittarioides and a comprehensive morphological description is provided, based on material from its entire range of distribution