819 research outputs found

    Synthesis of Distributed Longitudinal Control Protocols for a Platoon of Autonomous Vehicles

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    We develop a framework for control protocol synthesis for a platoon of autonomous vehicles subject to temporal logic specifications. We describe the desired behavior of the platoon in a set of linear temporal logic formulas, such as collision avoidance, close spacing or comfortability. The problem of decomposing a global specification for the platoon into distributed specification for each pair of adjacent vehicles is hard to solve. We use the invariant specifications to tackle this problem and the decomposition is proved to be scalable.. Based on the specifications in Assumption/Guarantee form, we can construct a two-player game (between the vehicle and its closest leader) locally to automatically synthesize a controller protocol for each vehicle. Simulation example for a distributed vehicles control problem is also shown

    The unified Skyrmion profiles and Static Properties of Nucleons

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    An unified approximated solution for symmetric Skyrmions was proposed for the SU(2) Skyrme model for baryon numbers up to 8,which take the hybrid form of a kink-like solution and that given by the instanton method. The Skyrmion profiles are examined by computing lowest soliton energy as well as the static properties of nucleons within the framework of collective quantization, with a good agreement with the exact numeric results. The comparisons with the previous computations as well as the experimental data are also given.Comment: 6 pages, 3 figures, 3 tables, Created by LaTex Syste

    Preparation of (Pb,Ba)TiO3 powders and highly oriented thin films by a sol-gel process

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    Solid solution Pb1-xBaxTiO3, with particular emphasis on Pb0.5Ba0.5TiO3, was prepared using a sol-gel process incorporating lead acetate trihydrate, barium acetate, and titanium isopropoxide as precursors, acetylacetone (2,4 pentanedione) as a chelating agent, and ethylene glycol as a solvent. The synthesis procedure was optimized by systematically varying acetylacetone: Ti and H2O:Ti molar ratios and calcination temperature. The resulting effects on sol and powder properties were studied using thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller analysis, and x-ray diffraction (XRD). Crystallization of the perovskite structure occurred at a temperature as low as 450 °C. Thin films were prepared by spin coating on (100) MgO. Pyrolysis temperature and heating rate were varied, and the resultant film properties investigated using field-emission scanning electron microscopy, atomic force microscopy, and XRD. Under optimized conditions, highly oriented films were obtained at a crystallization temperature of 600 °C

    Synthesis of Distributed Longitudinal Control Protocols for a Platoon of Autonomous Vehicles

    Get PDF
    We develop a framework for control protocol synthesis for a platoon of autonomous vehicles subject to temporal logic specifications. We describe the desired behavior of the platoon in a set of linear temporal logic formulas, such as collision avoidance, close spacing or comfortability. The problem of decomposing a global specification for the platoon into distributed specification for each pair of adjacent vehicles is hard to solve. We use the invariant specifications to tackle this problem and the decomposition is proved to be scalable.. Based on the specifications in Assumption/Guarantee form, we can construct a two-player game (between the vehicle and its closest leader) locally to automatically synthesize a controller protocol for each vehicle. Simulation example for a distributed vehicles control problem is also shown

    Numerical approximations for the tempered fractional Laplacian: Error analysis and applications

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    In this paper, we propose an accurate finite difference method to discretize the dd-dimensional (for d1d\ge 1) tempered integral fractional Laplacian and apply it to study the tempered effects on the solution of problems arising in various applications. Compared to other existing methods, our method has higher accuracy and simpler implementation. Our numerical method has an accuracy of O(hϵ)O(h^\epsilon), for uC0,α+ϵ(Ωˉ)u \in C^{0, \alpha+\epsilon} (\bar{\Omega}) if α<1\alpha < 1 (or uC1,α1+ϵ(Ωˉ)u \in C^{1, \alpha-1+\epsilon} (\bar{\Omega}) if α1\alpha \ge 1) with ϵ>0\epsilon > 0, suggesting the minimum consistency conditions. The accuracy can be improved to O(h2)O(h^2), for uC2,α+ϵ(Ωˉ)u \in C^{2, \alpha+\epsilon} (\bar{\Omega}) if α<1\alpha < 1 (or uC3,α1+ϵ(Ωˉ)u \in C^{3, \alpha - 1 + \epsilon} (\bar{\Omega}) if α1\alpha \ge 1). Numerical experiments confirm our analytical results and provide insights in solving the tempered fractional Poisson problem. It suggests that to achieve the second order of accuracy, our method only requires the solution uC1,1(Ωˉ)u \in C^{1,1}(\bar{\Omega}) for any 0<α<20<\alpha<2. Moreover, if the solution of tempered fractional Poisson problems satisfies uCp,s(Ωˉ)u \in C^{p, s}(\bar{\Omega}) for p=0,1p = 0, 1 and 0<s10<s \le 1, our method has the accuracy of O(hp+s)O(h^{p+s}). Since our method yields a (multilevel) Toeplitz stiffness matrix, one can design fast algorithms via the fast Fourier transform for efficient simulations. Finally, we apply it together with fast algorithms to study the tempered effects on the solutions of various tempered fractional PDEs, including the Allen-Cahn equation and Gray-Scott equations.Comment: 21 pages, 11 figures, 3 table

    Bulk Cr tips for scanning tunneling microscopy and spin-polarized scanning tunneling microscopy

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    A simple, reliable method for preparation of bulk Cr tips for Scanning Tunneling Microscopy (STM) is proposed and its potentialities in performing high-quality and high-resolution STM and Spin Polarized-STM (SP-STM) are investigated. Cr tips show atomic resolution on ordered surfaces. Contrary to what happens with conventional W tips, rest atoms of the Si(111)-7x7 reconstruction can be routinely observed, probably due to a different electronic structure of the tip apex. SP-STM measurements of the Cr(001) surface showing magnetic contrast are reported. Our results reveal that the peculiar properties of these tips can be suited in a number of STM experimental situations

    Comprehensive gait analysis of healthy older people: unveiling reasons for lack of long-distance walking

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    Many older adults do not adhere to the recommended physical activity levels. This study examines the gait changes upon long-distance walking among healthy older adults. Gait tests of 24 adults aged 65 or more were conducted at the baseline, at the end of 30 and 60 minutes of treadmill walk. Spatial temporal, kinematic and kinetic gait data were computed. Perceived level of exertion was evaluated for each subject. Ten subjects (Group B) perceived higher exertion level than the remaining fourteen subjects (Group A). After walking, group B had significant reductions in dominant-side ankle joint range of motion and power, suggesting lower-leg muscle fatigue, which appeared to be compensated by significantly increased non-dominant side knee and hip motions. These changes were not observed in Group A. Differences in gait parameters between Group A and B implied that some biomechanical factors might contribute to the lack of walking of some older adults
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