2,026 research outputs found
Determination of the Topology of a Directed Network
We consider strongly-connected directed networks of identical synchronous,
finite-state processors with in- and out-degree uniformly bounded by a network
constant. Via a straightforward extension of Ostrovsky and Wilkerson's
Backwards Communication Algorithm in [OW], we exhibit a protocol which solves
the Global Topology Determination Problem, the problem of having the root
processor map the global topology of a network of unknown size and topology,
with running time O(ND) where N represents the number of processors and D
represents the diameter of the network. A simple counting argument suffices to
show that the Global Topology Determination Problem has time-complexity Omega(N
logN) which makes the protocol presented asymptotically time-optimal for many
large networks.Comment: 9 pages, no figures, accepted to appear in IPDPS 2002 (unable to
attend), (journal version to appear in Information Processing Letters
Improved bounds and algorithms for graph cuts and network reliability
Karger (SIAM Journal on Computing, 1999) developed the first fully-polynomial
approximation scheme to estimate the probability that a graph becomes
disconnected, given that its edges are removed independently with probability
. This algorithm runs in time to obtain an
estimate within relative error .
We improve this run-time through algorithmic and graph-theoretic advances.
First, there is a certain key sub-problem encountered by Karger, for which a
generic estimation procedure is employed, we show that this has a special
structure for which a much more efficient algorithm can be used. Second, we
show better bounds on the number of edge cuts which are likely to fail. Here,
Karger's analysis uses a variety of bounds for various graph parameters, we
show that these bounds cannot be simultaneously tight. We describe a new graph
parameter, which simultaneously influences all the bounds used by Karger, and
obtain much tighter estimates of the cut structure of . These techniques
allow us to improve the runtime to , our results also
rigorously prove certain experimental observations of Karger & Tai (Proc.
ACM-SIAM Symposium on Discrete Algorithms, 1997). Our rigorous proofs are
motivated by certain non-rigorous differential-equation approximations which,
however, provably track the worst-case trajectories of the relevant parameters.
A key driver of Karger's approach (and other cut-related results) is a bound
on the number of small cuts: we improve these estimates when the min-cut size
is "small" and odd, augmenting, in part, a result of Bixby (Bulletin of the
AMS, 1974)
The RCA-F/Delta launch
The Delta 3924 launch vehicle configuration which incorporates the extended long tank Thor booster, nine Castor 4 strap-on motors, the AJ-118 second stage and the TE 364-4 third stage is to place into a synchronous transfer orbit, the second in a series of high-traffic capacity, 24 transponder communications satellites. Three days after launch, the satellite's apogee kick motor circularizes the orbit at geosynchronous altitude of 19,300 NM above the equator at approximately 128 degrees W longitude. The satellite can service commercial and government voice, digital and video communications requirements between Alaska and CONUS. The communications payload, mission requirements and spacecraft systems and subsystems are described
Shape-driven segmentation of the arterial wall in intravascular ultrasound images
Segmentation of arterial wall boundaries from intravascular images is an important problem for many applications in the study of plaque characteristics, mechanical properties of the arterial wall, its 3D reconstruction,
and its measurements such as lumen size, lumen radius, and wall radius. We present a shape-driven approach to segmentation of the arterial wall from intravascular ultrasound images in the rectangular domain. In a properly built
shape space using training data, we constrain the lumen and media-adventitia contours to a smooth, closed geometry, which increases the segmentation quality without any tradeoff with a regularizer term. In addition to a shape prior,
we utilize an intensity prior through a non-parametric probability density based image energy, with global image measurements rather than pointwise measurements used in previous methods. Furthermore, a detection step is included to address the challenges introduced to the segmentation process by side branches and calcifications. All these features greatly enhance our segmentation method. The tests of our algorithm on a large dataset demonstrate the effectiveness of our approach
Image data processing system requirements study. Volume 1: Analysis
Digital image processing, image recorders, high-density digital data recorders, and data system element processing for use in an Earth Resources Survey image data processing system are studied. Loading to various ERS systems is also estimated by simulation
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Shape-driven segmentation of the arterial wall in intravascular ultrasound images
Segmentation of arterial wall boundaries from intravascular images is an important problem for many applications in the study of plaque characteristics, mechanical properties of the arterial wall, its 3D reconstruction,
and its measurements such as lumen size, lumen radius, and wall radius. We present a shape-driven approach to segmentation of the arterial wall from intravascular ultrasound images in the rectangular domain. In a properly built
shape space using training data, we constrain the lumen and media-adventitia contours to a smooth, closed geometry, which increases the segmentation quality without any tradeoff with a regularizer term. In addition to a shape prior,
we utilize an intensity prior through a non-parametric probability density based image energy, with global image measurements rather than pointwise measurements used in previous methods. Furthermore, a detection step is included to address the challenges introduced to the segmentation process by side branches and calcifications. All these features greatly enhance our segmentation method. The tests of our algorithm on a large dataset demonstrate the effectiveness of our approach
Application of advanced technology to space automation
Automated operations in space provide the key to optimized mission design and data acquisition at minimum cost for the future. The results of this study strongly accentuate this statement and should provide further incentive for immediate development of specific automtion technology as defined herein. Essential automation technology requirements were identified for future programs. The study was undertaken to address the future role of automation in the space program, the potential benefits to be derived, and the technology efforts that should be directed toward obtaining these benefits
Flight data display studies for real time computer flight evaluation Final report
Real time displays for in-flight monitoring of Saturn launch vehicle
Data systems elements technology assessment and system specifications, issue no. 1
The ability to satisfy the objectives of future NASA Office of Applications Programs is dependent on technology advances in a number of areas of data systems. The technology of end-to-end data systems (space generator elements through ground processing, dissemination, and presentation, is examined in terms of state of the art, trends, and projected developments in the 1980 to 1985 timeframe. Capability is considered in terms of elements that are either commercially available or that can be implemented from commercially available components with minimal development
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