Finding a minimal cover for binary images: An optimal parallel algorithm

Given a black-and-white image, represented by an array of n × n binary-valued pixels, we wish to cover the black pixels with aminimal set of (possibly overlapping) maximal squares. It was recently shown that obtaining aminimum square cover for a polygonal binary image with holes is NP-hard. We derive an optimal parallel algorithm for theminimal square cover problem, which for any desired computation timeT in [logn,n] runs on an EREW-PRAM with (n/T) processors. The cornerstone of our algorithm is a novel data structure, the cover graph, which compactly represents the covering relationships between the maximal squares of the image. The size of the cover graph is linear in the number of pixels. This algorithm has applications to problems in VLSI mask generation, incremental update of raster displays, and image compression.The research reported here forms part of the author's doctoral dissertion, submitted to Cornell University in May 1989. This work was partially supported by NSF Grant DC1-86-02256, IBM Agreement 12060043, and ONR Contract N00014-83-K-0640. A preliminary version of this paper was presented at the 26th Annual Allerton Conference on Communications, Control, and Computing, Monticello, IL, September 28–30, 1988.     

Finding a minimal cover for binary images: An optimal parallel algorithm

Given a black-and-white image, represented by an array of √n × √n binary-valued pixels, we wish to cover the black pixels with aminimal set of (possibly overlapping) maximal squares. It was recently shown that obtaining aminimum square cover for a polygonal binary image with holes is NP-hard. We derive an optimal parallel algorithm for theminimal square cover problem, which for any desired computation timeT in [logn,n] runs on an EREW-PRAM with (n/T) processors. The cornerstone of our algorithm is a novel data structure, the cover graph, which compactly represents the covering relationships between the maximal squares of the image. The size of the cover graph is linear in the number of pixels. This algorithm has applications to problems in VLSI mask generation, incremental update of raster displays, and image compression.     

Adsorption and penetration of hydrogen in W: A first principles study

In BCC crystals, such as Tungsten (W), slippage has been observed on the (1 1 0) and (1 1 2) planes. In this work, hydrogen diffusion paths from three different W surfaces ((1 0 0), (1 1 0) and (1 1 2)) have been calculated using first principles density functional theory. Equilibrium sites for H at the surfaces are identified. The energetics for H penetration from the surfaces to the solute site in the bulk is calculated. It is found that for our low surface coverage of H (3.4 × 10¹⁴ H/cm²), approximately 2 eV is required for an H atom to penetrate any of the W surfaces considered in this study.     

The location of atomic hydrogen in NiTi alloy: A first principles study

A first principles density functional theory study to investigate the H defect in NiTi alloy is presented. We have determined the interstitial H atom position in bulk B2 phase NiTi alloy. H positions on both the Ti and Ni terminated NiTi surfaces are calculated. Surface adsorptions of H atom on Ni/Ti terminated surfaces are calculated for a low surface coverage of 1.96 × 10¹⁴ cm^?2. We have also calculated the penetration barrier energy for an H atom from the surface site to the bulk lattice site.     

Metallurgical Investigation of the Collapsed Front Structure of a Dragline in a Coal Mine

Journal of Failure Analysis and Prevention - A dragline is the largest mobile equipment on earth, and it is called the “kingpin” of any mine site. In this present investigation, a case...     

Performance comparison of a set of periodic and non-periodic tridiagonal solvers on SP2 and Paragon parallel computers

Various tridiagonal solvers have been proposed in recent years for different parallel platforms. In this paper, the performance of three tridiagonal solvers, namely, the parallel partition LU algorithm, the parallel diagonal dominant algorithm, and the reduced diagonal dominant algorithm, is studied. These algorithms are designed for distributed-memory machines and are tested on an Intel Paragon and an IBM SP2 machine. Measured results are reported in terms of execution time and speedup. Analytical studies are conducted for different communication topologies and for different tridiagonal systems. The measured results match the analytical results closely. In addition to addressing implementation issues, performance considerations such as problem sizes and models of speedup are also discussed. © 1997 John Wiley & Sons, Ltd.