A framework for multi-robot motion planning from temporal logic specifications

We propose a framework for the coordination of a network of robots with respect to formal requirement specifications expressed in temporal logics.A regular tessellation is used to partition the space of interest into a union of disjoint regular and equal cells with finite facets,and each cell can only be occupied by a robot or an obstacle.Each robot is assumed to be equipped with a finite collection of continuous-time nonlinear closed-loop dynamics to be operated in.The robot is then modeled as a hybrid automaton for capturing the finitely many modes of operation for either staying within the current cell or reaching an adjacent cell through the corresponding facet.By taking the motion capabilities into account,a bisimilar discrete abstraction of the hybrid automaton can be constructed.Having the two systems bisimilar,all properties that are expressible in temporal logics such as Linear-time Temporal Logic,Computation Tree Logic,and μ -calculus can be preserved.Motion planning can then be performed at a discrete level by considering the parallel composition of discrete abstractions of the robots with a requirement specification given in a suitable temporal logic.The bisimilarity ensures that the discrete planning solutions are executable by the robots.For demonstration purpose,a finite automaton is used as the abstraction and the requirement specification is expressed in Computation Tree Logic.The model checker Cadence SMV is used to generate coordinated verified motion planning solutions.Two autonomous aerial robots are used to demonstrate how the proposed framework may be applied to solve coordinated motion planning problems.     

NUMERICAL SIMULATIONS OF HIGHLY NONLINEAR STEADY AND UNSTEADY FREE SURFACE FLOWS

A numerical simulation model based on an open source Computational Fluid Dynamics (CFD) package-Open Field Operation and Manipulation (OpenFOAM) has been developed to study highly nonlinear steady and unsteady free surface flows. A two-fluid formulation is used in this model and the free surface is captured using the classical Volume Of Fluid (VOF) method. The incompressible Euler/Navier-Stokes equations are solved using a finite volume method on unstructured polyhedral cells. Both steady and unsteady free surface flows are simulated, which include: (1) a submerged NACA0012 2-D hydrofoil moving at a constant speed, (2) the Wigley hull moving at a constant speed, (3) numerical wave tank, (4) green water overtopping a fixed 2-D deck, (5) green water impact on a fixed 3-D body without or with a vertical wall on the deck. The numerical results obtained have been compared with the experimental measurements and other CFD results, and the agreements are satisfactory. The present numerical model can thus be used to simulate highly nonlinear steady and unsteady free surface flows.     

网络化制造的信息交换参考模型研究

结合目前的国际基础标准,建立了支持网络化制造的信息交换参考模型,阐述了其主要内容和功能.研究了参考模型中相关的标准协议集,同时给出了参考模型中协议集的实现技术.通过该参考模型可以较好地解决网络化制造中异构、分布式的信息交换和集成的部分问题.     

Cu-Bi合金偏析的原子模拟 Ⅰ.饱和偏析

本文研究了不同含量的Bi偏析于Cu的∑=5B(210)/〔001〕对称倾转晶界的原子结构.本文发现最重要的结构效应,是不同原子位置的偏析能的强烈不均匀性,以及在晶界区形成二维有序合金结构.并发现1.25单层是饱和偏析浓度.     

NUMERICAL SIMULATION OF BUBBLE FLOW INTERACTIONS

Bubble flow interaction can be important in many practical engineering applications. For instance, cavitation is a problem of interaction between nuclei and local pressure field variations including turbulent oscillations and large scale pressure variations. Various types of behaviours fundamentally depend on the relative sizes of the nuclei and the length scales of the pressure variations as well as the relative importance of bubble natural periods of oscillation and the characteristic time of the field pressure variations. Similarly, bubbles can significantly affect the performance of lifting devices or propulsors. We present here some fundamental numerical studies of bubble dynamics and deformation, then a practical method using a multi-bubble Surface Averaged Pressure (DF-Multi-SAP©) to simulate cavitation inception and scaling, and connect this with more precise 3-D simulations. This same method is then extended to the study of two-way coupling between a viscous compressible flow and a bubble population in the flow field.     

ACOUSTIC MEASUREMENTS BUBBLES IN BIOLOGICAL TIESSURE

An acoustic based instrument,the ABS Acoustic Bubble Spectrometer(R)(C)(ABS),was investigated for the detection and quantification of bubbles in biological media.These include viscoelastic media(blood),materials of varying density(bone in tissue),non-homogenous distribution of bubbles(intravenous bubbly flow),and bubbles migrating in tissue(decompression sickness,DCS).The performance of the ABS was demonstrated in a series of laboratory experiments.Validation of the code was performed using a viscoelastic polymer solution,Polyox,in which the bubble size distribution and void fraction were determined by ABS measurements and with image analysis of high speed videos.These tests showed that the accuracy of the ABS was not significantly affected by viscoelasticity for bubbles smaller than 200 microns.The ABS detection and measurement of non-homogenous bubble distributions was demonstrated using a bubbly flow through a simulated vein surrounded by tissue.The scatter of acoustic signals due to bones in the acoustic pathway was also investigated.These in-vitro experiments were done using meat(beef)as a tissue simulant.Decompression experiments were done using beef meat which was held underwater at high pressure(9.9 atm)then rapidly decompressed.Bubble size distributions and void fraction calculations in these experiments were then validated using image analysis of high speed video.In addition,preliminary experiments were performed with the US Navy Medical Research Center,demonstrating the utility of the modified ABS system in detecting the evolution of bubbles in swine undergoing decompression sickness(DCS).These results indicate that the ABS may be used to detect and quantify the evolution of bubbles in-vivo and aid in the monitoring of DCS.     

与环境烟气相关的挥发性有机物的特性

本项研究测定了环境烟气(ETS)中的多种挥发性有机物,在环境实验室中目标化合物的唯一来源就是ETS。实验室中的ETS是由燃吸肯塔基参考卷烟和其他8种市售卷烟产生的。在12轮试验中同时测定了30多种化合物。目标化合物分为3类,即:气相ETS标识物3乙基吡啶(简称3-EP)与烟碱、羰基化合物(包括甲醛)和挥发性有机化合物(简称VOCs)。利用环境实验室研究结果可以确定各种VOCs与3-EP(气相ETS标记物)的特征比率,另外还可以用来估测与ETS相关的VOCs的散发因子。总体说来,本项研究测得的特征比率与以往已经发表的实验室研究数据是一致的,这意味着,"真实"室内环境受多种来源的复杂的混合物影响。本项研究测定的特征比值也可以用于ETS目标化合物的定性和定量分析      

Consistent Analytic Embedded Atom Potential for Face-Centered Cubic Metals and Alloys

A consistent empirical embedded-atom potential that includes a long range force was developed for fcc (face-centered cubic) metals and alloys. The proposed potential for pure metals does not require modification of the initial function form when being applied to alloy systems. The potential parameters of this model were determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energies of the pure metals and the heats of solution of the binary alloys via an opti...     

自然需要一半：全球自然保护地新愿景

在全球尺度上,自然保护地的现状规模和"爱知目标11"不足以减缓生物多样性的下降趋势,因此亟须为全球自然保护地设立更高目标,并进一步扩大自然保护地面积。2009年,荒野基金会发起"自然需要一半"倡议(Nature Needs Half,NNH倡议),建议将地球至少50%的陆地和50%的海洋区域作为某种形式的自然保护地,并增强连通性。系统梳理并介绍了NNH倡议的背景和发展历程,从思想萌芽、正式提出和近期发展3个阶段分析了NNH倡议的主要内容。进一步从理论、政策和实践3个角度讨论了NNH倡议的可行性。最后,建议中国积极参与并在NNH倡议和制定"2020后全球生物多样性框架"中发挥更大作用。     

设计师的地球工程“工具箱”：危机给予风景园林师扭转、修复和再生地球气候的机会

当前，风景园林师的气候危机（CC）教育强调“弹性”（快速恢复能力）和适应力（应对CC影响的能力）。探索并倡导缓解方案，以期从根源上解决CC问题。该实践表明，风景园林专业地位独特，在缓解及修复气候变化方面发挥着重要作用。专家一致认为，应对气候变化不能仅依靠减排或减少化石燃料消耗量。联合国政府间气候变化专门委员会（IPCC）2019年发布的《全球增暖1.5 ℃特别报告》指出，过量二氧化碳已带来诸多全球变暖的后果，必须采取其他行动减少碳排量。大气脱碳的应对方案与风景园林专业直接相关，其中陆上气候应对方案是公认途径，可减少人为诱发的二氧化碳排放量。基于地球工程学（GE）探讨了一系列方法，总结可纳入风景园林师工具箱的诸多补救措施，并通过代表案例分析各种措施的实际应用。这些工具中有许多涉及设置不同规模的自然和生物系统，且需要相对较长的时间才能发挥生态效用。因此，除了短期策略，本研究也将讨论基于前沿技术的GE工具以避免灾难性影响，并提出在必要情况下，可以采用减缓与减排相结合的方式。