Computing the Number of Longest Common Subsequences

This note provides very simple, efficient algorithms for computing the number of distinct longest common subsequences of two input strings and for computing the number of LCS embeddings.Comment: 3 pages, LaTe

Bounds on the Number of Longest Common Subsequences

This paper performs the analysis necessary to bound the running time of known, efficient algorithms for generating all longest common subsequences. That is, we bound the running time as a function of input size for algorithms with time essentially proportional to the output size. This paper considers both the case of computing all distinct LCSs and the case of computing all LCS embeddings. Also included is an analysis of how much better the efficient algorithms are than the standard method of generating LCS embeddings. A full analysis is carried out with running times measured as a function of the total number of input characters, and much of the analysis is also provided for cases in which the two input sequences are of the same specified length or of two independently specified lengths.Comment: 13 pages. Corrected typos, corrected operation of hyperlinks, improved presentatio

Variational Principle in the Algebra of Asymptotic Fields

This paper proposes a variational principle for the solutions of quantum field theories in which the ``trial functions'' are chosen from the algebra of asymptotic fields, and illustrates this variational principle in simple cases.Comment: 15 pages, Latex, no figure

On the Area of Hypercube Layouts

This paper precisely analyzes the wire density and required area in standard layout styles for the hypercube. The most natural, regular layout of a hypercube of N^2 nodes in the plane, in a N x N grid arrangement, uses floor(2N/3)+1 horizontal wiring tracks for each row of nodes. (The number of tracks per row can be reduced by 1 with a less regular design.) This paper also gives a simple formula for the wire density at any cut position and a full characterization of all places where the wire density is maximized (which does not occur at the bisection).Comment: 8 pages, 4 figures, LaTe

Visible absorption spectra of sodium in sodium iodide

Visible absorption spectra of molten sodium in sodium iodid

Scattering by fluffy grains

There are indications (Greenberg et al., 1988), that fluffy (i.e., porous) particles are responsible for the observed 3.4 and 10 micron emissions of comet Halley. The absorption characteristics of small particles both solid and fluffy are needed in order to explain the Halley emissions. How isolated small solid particles react to an external radiation field is well known - the Rayleigh approximation. How these same small particles emit when assembled as fluffy aggregates in another question. To what degree are the emission spectra of isolated and aggregated particles comparable. In order to quantify the assertion that fluffy particles produce the observed Halley infrared emission features, the authors are performing calculations to determine the effect of porosity on the absorption characteristics of aggregates of interstellar grain-type particles. The calculations are based on an integral representation of the scattered electromagnetic field. Results are given with application to comet Halley

Reaction of O/1D/ with N2O

Reaction of excited oxygen with nitrous oxide 1 yielding nitrogen and oxyge

A comparative study of the continuum and emission characteristics of comet dust. 1: Are the silicates in Comet Halley and Kohoutek amorphous or crystalline

A continuum emission was subtracted from the 10 micron emission observed towards comets Halley and Kohoutek. The 10 micron excess emissions were compared with BN absorption and laboratory amorphous silicates. The results show that cometary silicates are predominantly amorphous which is consistent with the interstellar dust model of comets. It is concluded that cometary silicates are predominantly similar to interstellar silicates. For a periodic comet like Comet Halley, it is to be expected that some of the silicate may have been heated enough to convert to crystalline form. But apparently, this is only a small fraction of the total. A comparison of Comet Halley silicates with a combination of the crystalline forms observed in interplanetary dust particles (IPDs) seemed reasonable at first sight (Walker 1988, Brownlee 1988). But, if true, it would imply that the total silicate mass in Comet Halley dust is lower than that given by mass spectrometry data of Kissel and Krueger (1987). They estimated m sub org/m sub sil = 0.5 while using crystalline silicate to produce the 10 micron emission would give m sub org/m sub sil = 5 (Greenberg et al. 1988). This is a factor of 10 too high

Finding Connected Components on a Scan Line Array Processor

This paper provides a new approach to labeling the connected components of an n x n image on a scan line array processor (comprised of n processing elements). Variations of this approach yield an algorithm guaranteed to complete in o(n lg n) time as well as algorithms likely to approach O(n) time for all or most images. The best previous solutions require using a more complicated architecture or require Omega(n lg n) time. We also show that on a restricted version of the architecture, any algorithm requires Omega(n lg n) time in the worst case

The Fat-Pyramid and Universal Parallel Computation Independent of Wire Delay

This paper shows that a fat-pyramid of area Θ(A) requires only O(log A) slowdown to simulate any competing network of area A under very general conditions. The result holds regardless of the processor size (amount of attached memory) and number of processors in the competing networks as long as the limitation on total area is met. Furthermore, the result is valid regardless of the relationship between wire length and wire delay. We especially focus on elimination of the common simplifying assumption that unit time suffices to traverse a wire regardless of its length, since the assumption becomes more and more untenable as the size of parallel systems increases. This paper concentrates on simulation using transmission lines (wires along which bits can be pipelined) with the message routing schedule set up off line, but it also discusses the extension to on-line simulation. This paper also examines the capabilities of a fat-pyramid when matched against a substantially larger network and points out the surprising difficulty of doing such a comparison without the unit wire delay assumption