A high resolution solar atlas for fluorescence calculations

The characteristics required of a solar atlas to be used for studying the fluorescence process in comets are examined. Several sources of low resolution data were combined to provide an absolutely calibrated spectrum from 2250 A to 7000A. Three different sources of high resolution data were also used to cover this same spectral range. The low resolution data were then used to put each high resolution spectrum on an absolute scale. The three high resolution spectra were then combined in their overlap regions to produce a single, absolutely calibrated high resolution spectrum over the entire spectral range

Next-to-next-to-leading order O(αs4){\cal O}(\alpha_s^4) results for heavy quark pair production in quark--antiquark collisions: The one-loop squared contributions

We calculate the next-to-next-to-leading order ${\cal O}(\alpha_s^4)$ one-loop squared corrections to the production of heavy quark pairs in quark-antiquark annihilations. These are part of the next-to-next-to-leading order ${\cal O}(\alpha_s^4)$ radiative QCD corrections to this process. Our results, with the full mass dependence retained, are presented in a closed and very compact form, in the dimensional regularization scheme. We have found very intriguing factorization properties for the finite part of the amplitudes.Comment: 12 pages, 2 figures, electronic results file, abbreviation NNLO in Title and Abstract expanded, Summary expanded, reference updated, version to appear in Phys.Rev.

A Feature-Augmented Grammar for Automated Media Production

The IST Polymnia project is creating a fully automated system for personalised video generation, including content creation, selection and composition. This paper presents a linguistically motivated solution using context-free feature-augmented grammar rules to describe editing tasks and hence automate video editing. The solution is media and application independent

One-loop amplitudes for four-point functions with two external massive quarks and two external massless partons up to O(epsilon^2)

We present complete analytical ${\mathcal O}(\epsilon^2)$ results on the one-loop amplitudes relevant for the NNLO quark-parton model description of the hadroproduction of heavy quarks as given by the so-called loop-by-loop contributions. All results of the perturbative calculation are given in the dimensional regularization scheme. These one-loop amplitudes can also be used as input in the determination of the corresponding NNLO cross sections for heavy flavor photoproduction, and in photon-photon reactions.Comment: 25 pages, 6 figures in the text, Revtex, one reference added, minor improvements in the text, to appear in Phys.Rev.

15 years of comet photometry: A comparative analysis of 80 comets

In 1976 we began a program of narrowband photometry of comets that has encompassed well over 400 nights of observations. To date, the program has provided detailed information on 80 comets, 11 of which have been observed on multiple apparitions. In this paper we present the observed range of compositions (molecular production rate ratios) and dustiness (gas production compared with AF-rho) for a well sampled group of comets. Based on these results we present preliminary analysis of taxonomic groupings as well as the abundance ratios we associate with a 'typical' comet

Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2

On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05-4.83 micron wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ~10 kilometers of the coma collected 7 minutes and 23 minutes after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0 micron consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke's radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1 micron in size. The strong correlation between the water ice, dust, and CO2 spatial distribution supports the concept that CO2 gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-micron pure water ice grains at 1 AU, if velocities are near 0.5 m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-micron water ice particles [Hanner, 1981; Whipple, 1951], suggest that the observed water ice grains are likely aggregates.Comment: 51 pages, 12 figures, accepted for publication in Icaru

Subtropical Real Root Finding

We describe a new incomplete but terminating method for real root finding for large multivariate polynomials. We take an abstract view of the polynomial as the set of exponent vectors associated with sign information on the coefficients. Then we employ linear programming to heuristically find roots. There is a specialized variant for roots with exclusively positive coordinates, which is of considerable interest for applications in chemistry and systems biology. An implementation of our method combining the computer algebra system Reduce with the linear programming solver Gurobi has been successfully applied to input data originating from established mathematical models used in these areas. We have solved several hundred problems with up to more than 800000 monomials in up to 10 variables with degrees up to 12. Our method has failed due to its incompleteness in less than 8 percent of the cases

Z' Decays into Four Fermions

If a new $Z'$ is discovered with a mass $\sim 1 \ TeV$ at LHC/SSC, its (rare) decays into two charged leptons plus missing transverse energy will probe the $Z'$ coupling to the lepton doublet $(\nu,e)_L$ and to $W^+W^-$, allowing further discrimination among extended electroweak models.Comment: 9 pages plus 1 figure (not included but available), UG-FT-22/9

Software to compute infinitesimal symmetries of exterior differenial systems, with applications

A description is given of a software package to compute symmetries of partial differential equations, using computer algebra. As an application, the computation of higher-order symmetries of the classical Boussinesq equation is given leading to the recursion operator for symmetries in a straightforward way. Nonlocal symmetries for the Federbush model are obtained yielding the linearization of the model

Independent Set Reconfiguration in Cographs

We study the following independent set reconfiguration problem, called TAR-Reachability: given two independent sets $I$ and $J$ of a graph $G$, both of size at least $k$, is it possible to transform $I$ into $J$ by adding and removing vertices one-by-one, while maintaining an independent set of size at least $k$ throughout? This problem is known to be PSPACE-hard in general. For the case that $G$ is a cograph (i.e. $P_4$-free graph) on $n$ vertices, we show that it can be solved in time $O(n^2)$, and that the length of a shortest reconfiguration sequence from $I$ to $J$ is bounded by $4n-2k$, if such a sequence exists. More generally, we show that if $X$ is a graph class for which (i) TAR-Reachability can be solved efficiently, (ii) maximum independent sets can be computed efficiently, and which satisfies a certain additional property, then the problem can be solved efficiently for any graph that can be obtained from a collection of graphs in $X$ using disjoint union and complete join operations. Chordal graphs are given as an example of such a class $X$