43128338
Experiences with an architecture for intelligent, reactive agents
This paper describes an implementation of the 3T robot architecture which has been under development for the last eight years. The architecture uses three levels of abstraction and description languages which are compatible between levels. The makeup of the architecture helps to coordinate planful activities with real-time behaviours for dealing with dynamic environments. In recent years, other architectures have been created with similar attributes but two features distinguish the 3T architecture: (1) a variety of useful software tools have been created to help implement this architecture on multiple real robots; and (2) this architecture, or parts of it, have been implemented on a variety of very different robot systems using different processors, operating systems, effectors and sensor suites.
7547345
Path Planning Through Time and Space in Dynamic Domains
Realistic robot problems involve navigating the robot through time as well as space. The obstacles that a robot must avoid and the pathways on which it travels are subject to changes throughout time. These changes can occur in a predictable or unpredictable fashion. This paper presents an integrated route planning and spatial representation system that allows paths to be calculated in dynamic domains. The path planner finds the "best route" through a given n-dimensional space. The "best route" is defined as the path through space-time with the best score as determined by a set of user-defined evaluation functions. The algorithm takes into account the following: Capabilities of the robot executing generated plans, traversability of space, and interactions with both predictable and unpredictable dynamic objects. The route planning algorithm is highly parallel and can be run on an SIMD (Single Instruction Multiple Data) machine in 0(p) time, where p is the length of a path. In domains with unpredictable processes, this system may be run in an incremental fashion, allowing the robot to create real-time routes along the optimal path as described by its current information. This paper will discuss: Spatial representation, an SIMD algorithm for route planning in a dynamic domain, and results from an implementation on a traditional computer architecture.
657782
Experiences with an Architecture for Intelligent, Reactive Agents
This paper briefly describes a robot architecture that has been under development for the last eight years. This architecture uses several levels of abstraction and description languages that are compatible between levels. The makeup of the architecture helps to coordinate planful activities with real-time behaviors for dealing with dynamic environments. In recent years, many architectures have been created with similar attributes. The two features that distinguish this architecture from most of those are: 1) a variety of useful software tools have been created to help implement this architecture on multiple real robots; and 2) this architecture, or parts of it have been implemented on over half a dozen very different robot systems using a variety of processors, operating systems, effectors and sensor suites.
16341198
Global Symbolic Maps from Local Navigation
In order to navigate autonomously, most robot systems are provided with some sort of global terrain map. To make storage practical, these maps usually have a high-level symbolic representation of the terrain. The robot's symbolic map is then used to plan a local path. This paper describes a system which uses the reverse (and perhaps more natural) process. This system processes local sensor data in such a way as to allow efficient, reactive local navigation. A byproduct of this navigation process is an abstraction of the terrain information which forms a global symbolic terrain map of the terrain through which the robot has passed. Since this map is in the same format as that used by the local navigation system, the map is easy for the system to use, augment, or correct. Compared with the data from which the maps are created, the maps are very space efficient, and can be modified, or used for navigation in real-time. Experiments with this system, both in simulation, and with a real robot operating in natural terrain, are described.
39419808
A Twelve-Step Program to More Efficient Robotics
Sensor abuse is a serious and debilitating condition. However, one must remember that it is a disease, not a crime.1 As such, it can be treated. This article presents a case study in sensor abuse. This particular subject was lucky enough to pull himself out of his pitiful condition, but others are not so lucky. The article also describes a 12- step behavior-modification program modeled on this and other successful case studies.
303726
Simplified navigation and traverse planning for a long-range planetary rover
This paper presents the sensor and control system for SR2, a planetary rover prototype capable of km+/day traverses through Mars-like terrain. The control system described allowed the rover to successfully navigate Mars-like terrain given a set of way-points spaced approximately 100 m apart. The control system uses input from a variety of sensors including heading, roll, pitch, an array of proximity sensors, voltage and current sensors, and a depth from stereo camera system. The control system is adequate, when combined with the rover's mobility system to make its way over or around almost all hazards a rover is likely to encounter, and to know when it is getting diverted so far off course that it needs to ask for help. In a recent field test, the robot autonomously navigated through 1.3 km of Mars like terrain to reach its goal. The SR2 is a solar powered, four-wheeled rover that masses 21 kg and fits inside a 90/spl times/65/spl times/40 cm envelope.
9016351
A framework for evaluating computer supported collaborative learning
Starting from some central issues of Information and Communications Technology (ICT) in learning and of collaborative learning, this paper postulates a composite framework for evaluating learning environments. Using the framework, one scenario is described and analysed. The framework identifies where ICT in learning (e-learning) may be enhanced and where ICT may be difficult for students. Some conclusions are made relevant to the design of ICT learning environments. Areas for future research are suggested.
9952136
Using a distributed single address space operating system to support modern cluster computing
Recent 64-bit microprocessors have made a huge 18.4 quintillion byte address space potentially available to programs. This has led to the design of operating systems that provide a single virtual address space in which all code and data reside in and across all levels of storage and all nodes of a distributed system. These operating systems, called single address space operating systems (SASOSs), have characteristics that can be used to support modern cluster computing in a distributed system in ways that provide an improved program development environment and higher performance than is available from conventional operating systems. Sombrero, our SASOS design, makes use of its hardware support for object-grained protection, separate thread-related protection domains and implicit protection domain crossing to provide support for modern cluster computing which is not available in SASOSs built on stock processors. Its design, which provides direct system-level support for object-oriented programming, includes a number of features targeted specifically at modern cluster computing.
14544430
Specifying Theorem Provers in a Higher-Order Logic Programming Language
Since logic programming systems directly implement search and unification and since these operations are essential for the implementation of most theorem provers, logic programming languages should make ideal implementation languages for theorem provers. We shall argue that this is indeed the case if the logic programming language is extended in several ways. We present an extended logic programming language where first-order terms are replaced with simply-typed λ-terms, higher-order unification replaces first-order unification, and implication and universal quantification are allowed in queries and the bodies of clauses. This language naturally specifies inference rules for various proof systems. The primitive search operations required to search for proofs generally have very simple implementations using the logical connectives of this extended logic programming language. Higher-order unification, which provides sophisticated pattern matching on formulas and proofs, can be used to determine when and at what instance an inference rule can be employed in the search for a proof. Tactics and tacticals, which provide a framework for high-level control over search, can also be directly implemented in this extended language. The theorem provers presented in this paper have been implemented in the higher-order logic programming language λProlog.
1440056
Concerning the achromatic number of graphs
Abstract The achromatic number of a graph G is the largest number of colors that can be assigned to the vertices of G so that (i) adjacent vertices are assigned different colors, and (ii) any two different colors are assigned to some pair of adjacent vertices. We study the achromatic number from the point of view of computational complexity. We show that, for each fixed integer n , there is an algorithm which, for an arbitrary graph G , determines in time O (| E ( G )|) whether the achromatic number of G is at least n . In contrast to this, we show that when n is part of the input, the problem is NP-complete even when restricted to bipartite graphs. The complexity of determining the achromatic number of a tree is unknown. We present polynomial algorithms to solve this problem for several classes of trees, and provide upper bounds on the achromatic number of a tree in terms of the maximum degree and the number of edges.
5486748
Scaling internet routers using optics
Routers built around a single-stage crossbar and a centralized scheduler do not scale, and (in practice) do not provide the throughput guarantees that network operators need to make efficient use of their expensive long-haul links. In this paper we consider how optics can be used to scale capacity and reduce power in a router. We start with the promising load-balanced switch architecture proposed by C-S. Chang. This approach eliminates the scheduler, is scalable, and guarantees 100% throughput for a broad class of traffic. But several problems need to be solved to make this architecture practical: (1) Packets can be mis-sequenced, (2) Pathological periodic traffic patterns can make throughput arbitrarily small, (3) The architecture requires a rapidly configuring switch fabric, and (4) It does not work when linecards are missing or have failed. In this paper we solve each problem in turn, and describe new architectures that include our solutions. We motivate our work by designing a 100Tb/s packet-switched router arranged as 640 linecards, each operating at 160Gb/s. We describe two different implementations based on technology available within the next three years.