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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 4 (1989), S. 329-341 
    ISSN: 1432-0541
    Keywords: Round-robin token-passing ; Mobile communication ; Euclidean Traveling Salesman tours ; Approximation algorithms ; Incremental corrections
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We present a distributed approximation algorithm for the Traveling Salesman Problem (TSP) in networks that use a broadcast, multiaccess communication channel. The application for which the algorithm was originally designed is maintaining a short token-passing path (which means low scheduling overhead) in radio networks with mobile nodes. The algorithm is adaptive in the sense that it shifts gradually between performing a slight correction of an existing tour and recomputing one “from scratch.” It can thus be viewed as a generalization, or extension, of conventional TSP algorithms. The proposed algorithm guarantees the same worst-case tour length as the one guaranteed by any conventional “from scratch” algorithm, yet it is capable of taking advantage of certain node layouts (e.g., geographically clustered nodes) to reduce the cost of computing the path. The correction algorithm is suitable for dynamic graphs with slowly changing edge weights, and for which a Traveling Salesman tour (optimal or approximate) has previously been computed and is “deteriorating” with time due to the weight changes. The algorithm can be used to “refresh” the tour whenever it deteriorates beyond a given level, and thus maintain a reasonable average tour length at relatively low computation and communication costs. For a Euclidean graph withn nodes laid out in a bounded area with diameterD, the maximal length of the tour produced by the algorithm is proportional toD√n, like the maximal length of an optimal tour in that graph (the two differ by a factor of 2 at the worst case).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Distributed computing 2 (1987), S. 139-148 
    ISSN: 1432-0452
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Two distributed algorithms are presented for a network using a common communication channel (e.g. radio) in which all nodes are within signal range and in line of sight of each other: (a) an algorithm to compute all $$\left( {\begin{array}{*{20}c} N \\ 2 \\ \end{array} } \right)$$ internode distances (in terms of propagation delays) in the network. the algorithm requires only 2 messages per node, and provides each node with the distances to all other nodes. (b) An algorithm for constructing a minimum-weight spanning tree (MST) in such a network. This algorithm starts out with the information provided by (a) and ends with each node possessing the explicit knowledge of the full MST. The algorithm requires at most log2 N messages per node. The internal processing in each node needsO(N logN) time andO(N) space. All messages required by (a) and (b) contain at most one edge weight plus 2 log2 N bits. Some possible applications of the algorithms are: position-location, tuning acknowledgement time-out mechanisms, tuning the scheduling functions of access protocols that are sensitive to individual internode propagation delays, and selecting performance effective transmission sequences for round robin access protocols.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1989-06-01
    Print ISSN: 0178-4617
    Electronic ISSN: 1432-0541
    Topics: Computer Science , Mathematics
    Published by Springer
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  • 4
    Publication Date: 2013-08-31
    Description: This paper describes a study conducted by NASA Ames Research Center (ARC) in collaboration with the Jet Propulsion Laboratory (JPL), Pasadena, California on the image acceptability of the Galileo Low Gain Antenna mission. The primary objective of the study is to determine the impact of the Integer Cosine Transform (ICT) compression algorithm on Galilean images of atmospheric bodies, moons, asteroids and Jupiter's rings. The approach involved fifteen volunteer subjects representing twelve institutions involved with the Galileo Solid State Imaging (SSI) experiment. Four different experiment specific quantization tables (q-table) and various compression stepsizes (q-factor) to achieve different compression ratios were used. It then determined the acceptability of the compressed monochromatic astronomical images as evaluated by Galileo SSI mission scientists. Fourteen different images were evaluated. Each observer viewed two versions of the same image side by side on a high resolution monitor, each was compressed using a different quantization stepsize. They were requested to select which image had the highest overall quality to support them in carrying out their visual evaluations of image content. Then they rated both images using a scale from one to five on its judged degree of usefulness. Up to four pre-selected types of images were presented with and without noise to each subject based upon results of a previously administered survey of their image preferences. Fourteen different images in seven image groups were studied. The results showed that: (1) acceptable compression ratios vary widely with the type of images; (2) noisy images detract greatly from image acceptability and acceptable compression ratios; and (3) atmospheric images of Jupiter seem to have higher compression ratios of 4 to 5 times that of some clear surface satellite images.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Goddard Space Flight Center, The 1994 Space and Earth Science Data Compression Workshop; p 3-10
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: This paper describes a study conducted for the Jet Propulsion Laboratory, Pasadena, California, using 15 evaluators from 12 institutions involved in the Galileo Solid State Imaging (SSI) experiment. The objective of the study was to determine the impact of integer cosine transform (ICT) compression using specially formulated quantization (q) tables and compression ratios on acceptability of the 800 x 800 x 8 monochromatic astronomical images as evaluated visually by Galileo SSI mission scientists. Fourteen different images in seven image groups were evaluated. Each evaluator viewed two versions of the same image side by side on a high-resolution monitor; each was compressed using a different q level. First the evaluators selected the image with the highest overall quality to support them in their visual evaluations of image content. Next they rated each image using a scale from one to five indicating its judged degree of usefulness. Up to four preselected types of images with and without noise were presented to each evaluator.
    Keywords: ASTRONOMY
    Type: NASA-TP-3482 , A-94068 , NAS 1.60:3482
    Format: application/pdf
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