13,554 research outputs found
Self-employment and the Paradox of the Contented Female Worker
Acknowledgements: Thanks to seminar participants at the University of Aberdeen and John Heywood for helpful comments.Publisher PD
Integrating factors for second order ODEs
A systematic algorithm for building integrating factors of the form mu(x,y),
mu(x,y') or mu(y,y') for second order ODEs is presented. The algorithm can
determine the existence and explicit form of the integrating factors themselves
without solving any differential equations, except for a linear ODE in one
subcase of the mu(x,y) problem. Examples of ODEs not having point symmetries
are shown to be solvable using this algorithm. The scheme was implemented in
Maple, in the framework of the "ODEtools" package and its ODE-solver. A
comparison between this implementation and other computer algebra ODE-solvers
in tackling non-linear examples from Kamke's book is shown.Comment: 21 pages - original version submitted Nov/1997. Related Maple
programs for finding integrating factors together with the ODEtools package
(versions for MapleV R4 and MapleV R5) are available at
http://lie.uwaterloo.ca/odetools.ht
Airborne observations of methane in Comet Kohoutek
The experiment is described for airborne observations of Comet Kohoutek using an infrared tilting-filter photometer. Preliminary analysis of the data established an upper limit to the Comet's fluorescence radiation in methane lines at 3.3 microns
The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
The 9.7-micron silicate absorption profile in the interstellar medium
provides important information on the physical and chemical composition of
interstellar dust grains. Measurements in the Milky Way have shown that the
profile in the diffuse interstellar medium is very similar to the amorphous
silicate profiles found in circumstellar dust shells around late M stars, and
narrower than the silicate profile in denser star-forming regions. Here, we
investigate the silicate absorption profile towards the very heavily obscured
nucleus of NGC 4418, the galaxy with the deepest known silicate absorption
feature, and compare it to the profiles seen in the Milky Way. Comparison
between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger
aperture spectrum obtained from the Spitzer archive indicates that the former
isolates the nuclear emission, while Spitzer detects low surface brightness
circumnuclear diffuse emission in addition. The silicate absorption profile
towards the nucleus is very similar to that in the diffuse ISM in the Milky Way
with no evidence of spectral structure from crystalline silicates or silicon
carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres
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