Quiver Presentations for Descent Algebras of Exceptional Type

The descent algebra of a finite Coxeter group $W$ is a basic algebra, and as such it has a presentation as quiver with relations. In recent work, we have developed a combinatorial framework which allows us to systematically compute such a quiver presentation for a Coxeter group of a given type. In this article, we use that framework to determine quiver presentations for the descent algebras of the Coxeter groups of exceptional or non-crystallographic type, i.e., of type $E_6$, $E_7$, $E_8$, $F_4$, $H_3$, $H_4$ or $I_2(m)$.Comment: 25 pages, 10 figure

Variability and Evolution in Systems of Systems

In this position paper (1) we discuss two particular aspects of Systems of Systems, i.e., variability and evolution. (2) We argue that concepts from Product Line Engineering and Software Evolution are relevant to Systems of Systems Engineering. (3) Conversely, concepts from Systems of Systems Engineering can be helpful in Product Line Engineering and Software Evolution. Hence, we argue that an exchange of concepts between the disciplines would be beneficial.Comment: In Proceedings AiSoS 2013, arXiv:1311.319

Reading in perspective : what real cops and pretend burglars look for in a story

Bibliography: leaves 26-27Supported in part by the National Institute of Education under contract no. US-NIE-C-400-76-0116 and by the Advanced Research Projects Agency under contract no. N00123-C-062

Non-thermal line-broadening in solar prominence

We show that the line broadening in quiescent solar prominences is mainly due to non-thermal velocities. We have simultaneously observed a wide range of optically thin lines in quiescent prominences, selected for bright and narrow Mg\,b emission without line satellites from macro-shifts. We find a ratio of reduced widths of H-gamma and H-delta of 1.05 +-0.03 which can hardly be attributed to saturation, since both are optically thin for the prominences observed: tau(gamma)<0.3 ; tau(delta)<0.15. We confirm the ratio of reduced widths of He4772(triplet) and He5015(singlet of 1.1 +-0.05 at higher significance and detect a width ratio of Mgb2 and Mg4571 (both from the triplet system) of 1.3 +-0.1. The discrepant widths of lines from different atoms, and even from the same atom, cannot be represented by a unique pair [T_kin ; V_nth]. Values of T_kin deduced from observed line radiance using models, indicate low temperatures down to T_kin~5000K. Non-thermal velocities, related to different physical states of the respective emitting prominence region, seem to be the most important line broadening mechanism

A Method for the Rapid Cultivation of Desulfovibrio aestuarii on Filter Membranes

The cultivation of sulfate-reducing bacteria on agar plates is a somewhat involved and time-consuming process. This is partly due to the requirement for fairly strict anaerobic conditions but mainly because of the length of the incubation period which may vary from 6 days to weeks with the resulting delay of the required information. The work reported herein was undertaken in an attempt to apply the advantageous features of the membrane filter method to the detection of anaerobic organisms. As originally developed, the membrane filter (Goetz and Tsuneishi, 1951; Clark et al., 1951) permits the recovery of small numbers of organisms from large volumes of water and the rapid cultivation of many aerobic bacteria. The ultimate purpose was to develop a method which would not require more complex manipulation than the membrane procedure according to Standard Methods for the Examination of Water, Sewage, and Industrial Wastes (A.P.H.A. 1955) and to reduce the incubation period for anaerobic bacteria

The Complexity of Datalog on Linear Orders

We study the program complexity of datalog on both finite and infinite linear orders. Our main result states that on all linear orders with at least two elements, the nonemptiness problem for datalog is EXPTIME-complete. While containment of the nonemptiness problem in EXPTIME is known for finite linear orders and actually for arbitrary finite structures, it is not obvious for infinite linear orders. It sharply contrasts the situation on other infinite structures; for example, the datalog nonemptiness problem on an infinite successor structure is undecidable. We extend our upper bound results to infinite linear orders with constants. As an application, we show that the datalog nonemptiness problem on Allen's interval algebra is EXPTIME-complete.Comment: 21 page