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The dynamics and control of tendon driven three degree of freedom shoulder joint are studied. A control scheme consisting of two phases has been developed. In the first phase, approximation of the time optimal control trajectory was applied open to the loop to the system. In the second phase a closed loop linear feedback law was employed to bring the system to the desired final state and to maintain it there.
This proposal addresses some of the biophysical events possibly underlying fast activity-dependent changes in synaptic efficiency. Dendritic spines in the cortex have attracted increased attention over the last years as a possible locus of cellular plasticity given the large number of studies reporting a close correlation between presynaptic activity (or lack of thereof) and changes in spine shape. This is highlighted by recent reports, showing that the spine cytoplasm contains high levels of actin. Moreover, it has been demonstrated that a high level of intracellular free calcium Ca squared positive, is a prerequisite for various forms of synaptic potentiation. We propose a series of plausible steps, linking presynaptic electrical activity at dendritic spines with a short lasting change in spine geometry. Specificall...
This is a primer on extended Gaussian Images. Extended Gaussian Images are useful for representing the shapes of surfaces. They can be computed easily from: 1. Needle maps obtained using photometric stereo, or 2. Depth maps generated by ranging devices or stereo. Importantly, they can also be determined simply from geometric models of the objects. Extended Gaussian images can be of use in at least two of the tasks facing a machine vision system. 1. Recognition, and 2. Determining the attitude in space of an object. Here, the extended Gaussian image is defined and some of its properties discussed. An elaboration for non-convex objects is presented and several examples are shown.
An important skill in programming is being able to visualize the operation of procedures, both for constructing programs and debugging them. Tinker is a programming environment for Lisp that enables the programmer to "see what the program is doing" while the program is being constructed, by displaying the result of each step in the program on representative examples. To help the reader visualize the operation of Tinker itself, an example is presented of how he or she might use Tinker to construct an alpha-beta tree search program.
This paper describes some problems and opportunities associated with conceptual modeling for the kind of "open systems" we foresee must and will be increasingly recognized as a central line of computer system development. Computer applications will be based on communication between sub-systems which will have been developed separately and independently. Some of the reasons for independent development are the following: competition, different goals and responsibilities, economics, and geographical distribution. We must deal with all the problems that arise from this conceptual disparity of sub-systems which have been independently developed. Sub-systems will be open-ended and incremental ??dergoing continual evolution. There are no global objects. The only thing that all the various sub-systems hold in common is the a...
An efficient algorithm is presented for the calculation of the inverse kinematic accelerations for a 6 degree-of-freedom manipulator with a spherical wrist. The inverse kinematic calculation is shown to work synergistically with the inverse dynamic calculation, producing kinematic parameters needed in the recursive Newton-Euler dynamics formulation. Additional savings in the dynamics computation are noted for a class of kinematically well-structured manipulators such as spherical-wrist arms and for manipulators with simply-structured inertial parameters.
An extremum principle is developed that determines three-dimensional surface orientation from a two-dimensional contour. The principle maximizes the ratio of the area to the square of the perimeter, a measure of the compactness or symmetry of the three-dimensional surface. The principle interprets regular figures correctly and it interprets skew symmetries as oriented real symmetries. The maximum likelihood method approximates the principle on irregular figures, but we show that it consistently overestimates the slant of an ellipse.
This paper describes a system which locates and grasps doughnut shaped parts from a pile. The system uses photometric stereo and binocular stereo as vision input tools. Photometric stereo is used to make surface orientation measurements. With this information the camera field is segmented into isolated regions of continuous smooth surface. One of these regions is then selected as the target region. The attitude of the physical object associated with the target region is determined by histograming surface orientations over that region and comparing with stored histograms obtained from prototypical objects. Range information, not available from photometric stereo is obtained by the PRISM binocular stereo system. A collision-free grasp configuration and approach trajectory is computed and executed using the attitude, an...
A complete theory of object recognition is an impossibility ??t simply because of the multiplicity of visual cues we exploit in elegant coordination to identify an object, but primarily because recognition involves fixation of belief, and anything one knows may be relevant. We finesse this obstacle with two moves. The first restricts attention to one visual cue, the shapes of objects; the second restricts attention to one problem, the initial guess at the identity of an object. We propose that the visual system decomposes a shape into parts, that it does so using a rule defining part boundaries rather than part shapes, that the rule exploits a uniformity of nature ??ransversality, and that parts with their descriptions and spatial relations provide a first index into a memory of shapes. These rules lead to a more compr...
Chaosnet is a local network, that is, a system for communication among a group of computers located within about 1000 meters of each other. Originally developed by the Artificial Intelligence Laboratory as the internal communications medium of the Lisp Machine system, it has since come to be used to link a variey of machines around MIT and elsewhere.
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