Tractable model discrimination for safety–critical systems with disjunctive and coupled constraints

This paper considers the model discrimination problem among a finite number of models in safety–critical systems that are subjected to constraints that can be disjunctive and where state and input constraints can be coupled with each other. In particular, we consider both the optimal input design problem for active model discrimination that is solved offline as well as the online passive model discrimination problem via a model invalidation framework. To overcome the issues associated with non-convex and generalized semi-infinite constraints due to the disjunctive and coupled constraints, we propose some techniques for reformulating these constraints in a computationally tractable manner by leveraging the Karush–Kuhn–Tucker (KKT) conditions and introducing binary variables, thus recasting the active and passive model discrimination problems into tractable mixed-integer linear/quadratic programming (MILP/MIQP) problems. When compared with existing approaches, our method is able to obtain the optimal solution and is observed in simulations to also result in less computation time. Finally, we demonstrate the effectiveness of the proposed active model discrimination approach for estimating driver intention with disjunctive safety constraints and state–input coupled curvature constraints, as well as for fault identification.     

Lagrangian formulation of the linear autonomous magnetization dynamics in spin-torque auto-oscillators

A Lagrangian formalism is used to find steady-state solution of the Landau-Lifshitz-Gilbert-Slonczewski equation corresponding to the linear autonomous dynamics of a magnetic auto-oscillatory system subject to the action of a spin-polarized electric current. In such a system, two concurrent dissipative mechanisms, arising from the positive intrinsic dissipation and the negative current-induced one, take place simultaneously and make the excitation of a steady precessional motion of the magnetization vector conceivable. The proposed formulation leads to the definition of a complex generalized non-Hermitian Eigenvalue problem, both in the case of a macrospin model and in the more general case of an ensemble of magnetic particles interacting each other through magnetostatic and exchange interactions. This method allows to identify the spin-wave normal modes which become unstable in the presence of the two competing dissipative contributions and provides an accurate estimation of the value of the excitation threshold current.     

培养学生的自主学习能力——北京大学普通化学英文小班课的尝试

简要介绍了北京大学普通化学英文小班课的教学情况,以及在培养学生自主学习能力方面进行的尝试。课程强调一对一启发式教育,力求激发学生自主探究问题的兴趣,注重培养学生的科研基本素质,引导性地提升学生全方位的学习能力。     

Comparative study of chained systems theory and fuzzy logic as a solution for the nonlinear lateral control of a road vehicle

This paper presents a comparative study of different lateral controllers applied to the autonomous steering of automobiles. The nonlinear nature of vehicle dynamics makes it a challenging problem in the Intelligent Transportation Systems (ITS) field, as long as a stable, accurate controller is compulsorily needed in order to ensure safety during navigation. The problem has been tackled under two different approaches. The first one is based on chained systems theory, while the second controller relies on fuzzy logic. A comparative analysis has been carried out based on the results achieved in practical trials. Real tests were conducted using a DGPS-driven electric Citroen Berlingo in a private test circuit located at the Industrial Automation Institute of the CSIC (Arganda del Rey, Madrid). The final results and conclusions are presented.     

On Nonexistence of Algebraic Curve Solutions to Second-order Polynomial Autonomous Systems Over the Complex Field

In this paper, by using the method of algebraic analysis, the results in our previous work are generalized. These results are of importance in the qualitative theory of polynomial autonomous systems.     

Multimodal Self-sustainable Autonomous Locomotions of Light-driven Seifert Ribbon Actuators based on Liquid Crystal Elastomers

Multimodal self-sustainable autonomous locomotions integrated into one individual system, are high-level intelligent behavioral characteristics of living organisms and are the scientific hotspot of bionic soft actuators. Here, we report a light-fueled soft actuator with multimodal self-sustainable movements based on a Seifert ribbon bounded by a Hopf link. The Seifert ribbon actuator can self-sense the illumination area adjustment, and the actuation component becomes either a discontinuous strip-like structure or a continuous toroidal structure, which can realize adaptive switches between self-sustained oscillatory and rotary motions. The two motion modes are applied to the self-oscillatory piezoelectric generation and self-rotational work multiplication of cargo transport, respectively. The unique smartness of Seifert surface topology advances the level of actuation intelligence with broad implications for the adaptability, multifunctionality, and autonomy of soft robots.     

Existence of periodic orbits for high-dimensional autonomous systems

We give a result on existence of periodic orbits for autonomous differential systems with arbitrary finite dimension. It is based on a Poincaré-Bendixson property enjoyed by a new class of monotone systems introduced in [L.A. Sanchez, Cones of rank 2 and the Poincaré-Bendixson property for a new class of monotone systems, J. Differential Equations 216 (2009) 1170-1190]. A concrete application is done to a scalar differential equation of order 4.     

Polygon exploration with time-discrete vision

With the advent of autonomous robots with two- and three-dimensional scanning capabilities, classical visibility-based exploration methods from computational geometry have gained in practical importance. However, real-life laser scanning of useful accuracy does not allow the robot to scan continuously while in motion; instead, it has to stop each time it surveys its environment. This requirement was studied by Fekete, Klein and Nüchter for the subproblem of looking around a corner, but until now has not been considered in an online setting for whole polygonal regions.We give the first algorithmic results for this important optimization problem that combines stationary art gallery-type aspects with watchman-type issues in an online scenario: We demonstrate that even for orthoconvex polygons, a competitive strategy can be achieved only for limited aspect ratio A (the ratio of the maximum and minimum edge length of the polygon), i.e., for a given lower bound on the size of an edge; we give a matching upper bound by providing an O(logA)-competitive strategy for simple rectilinear polygons, using the assumption that each edge of the polygon has to be fully visible from some scan point.     

Enhanced vision for adverse weather aircraft landing

Landing in poor weather is a crucial problem for the air transportation system of the future. To aid the pilots for these conditions several solutions have been suggested and/or implemented including instrument landing system(ILS) and microwave landing system(MLS) that put the responsibility of the landing to a large extent in the hands of the airport facilities. These systems even though useful are not available due to their high costs except in few major metropolitan airports. This shortcoming has generated interest in providing all weather capabilities not on the landing facility but on the vehicle itself. The Synthetic Vision System Technology Demonstration sponsored by the United States Federal Aviation Administration(FAA) and the US Air Force represents an effort to respond to the above needs[1,2]. In this paper we present a summary of a typical synthetic vision system. This system consists of a scanning 35GHz radar a scanning antenna, a signal/image processor and a head up display(HUD). The pilot is presented a final perspective image of the scene sensed by the radar with associated flight guidance symbology. This systems is implemented in real time hardware and has been under going tower and flight testing under a variety of weather conditions since early 1992.