HI Emission and Absorption in the Southern Galactic Plane Survey

We present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325.5 deg < l < 333.5 deg; -0.5 deg < b < 3.5 deg) were completed in December 1998. Single dish observations of the full survey region (253 deg < l < 358 deg; |b| <1 deg) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS HI data with particular attention to the smallest and largest scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent HI shells. On the small scale, we note extremely compact, cold clouds seen in HI self-absorption. We explore how these two classes of objects probe opposite ends of the HI spatial power spectrum.Comment: 9 pages, 3 embedded postscript & 4 jpeg figures. Presented at the Astronomical Society of Australia, Hobart, Tasmania, July 4-7 2000. To appear in PASA Vol. 18(1

Dark Energy as a Born-Infeld Gauge Interaction Violating the Equivalence Principle

We investigate the possibility that dark energy does not couple to gravitation in the same way than ordinary matter, yielding a violation of the weak and strong equivalence principles on cosmological scales. We build a transient mechanism in which gravitation is pushed away from general relativity by a Born-Infeld gauge interaction acting as an "Abnormally Weighting" (dark) Energy. This mechanism accounts for the Hubble diagram of far-away supernovae by cosmic acceleration and time variation of the gravitational constant while accounting naturally for the present tests on general relativity.Comment: 5 pages, 3 figures, sequel of Phys. Rev. D 73 023520 (2006), to appear in Physical Review Letter

Supergiant Shells and Molecular Cloud Formation in the LMC

We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between HI and 12CO(J=1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects (~70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that ~12-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to ~4-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.Comment: 14 pages, 6 figures. Accepted for publication in Ap

An exploratory study of the hard X-ray variability properties of PG quasars with RXTE

We have monitored with the RXTE PCA the variability pattern of the 2-20 keV flux in four PG quasars (QSOs) from the Laor et al. (1994) sample. Six observations of each target at regular intervals of 1 day were performed. The sample comprises objects with extreme values of Balmer line width (and hence soft X-ray steepness) and spans about one order of magnitude in luminosity. The most robust result is that the variability amplitude decreases as energy increases. Several options for a possible ultimate driver of the soft and hard X-ray variability, such as the influx rate of Comptonizing relativistic particles, instabilities in the accretion flow or the number of X-ray active sites, are consistent with our results.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

The Supershell-Molecular Cloud Connection in the Milky Way and Beyond

The role of large-scale stellar feedback in the formation of molecular clouds has been investigated observationally by examining the relationship between HI and 12CO(J=1-0) in supershells. Detailed parsec-resolution case studies of two Milky Way supershells demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. Recent results on supergiant shells in the LMC suggest that while they do indeed help to organise the ISM into over-dense structures, their global contribution to molecular cloud formation is of the order of only ~10%.Comment: Proceedings of IAUS 292 - Molecular Gas, Dust, and Star Formation in Galaxies, eds. T. Wong & J. Ott. 4 pages, 3 figure

Courant-like brackets and loop spaces

We study the algebra of local functionals equipped with a Poisson bracket. We discuss the underlying algebraic structures related to a version of the Courant-Dorfman algebra. As a main illustration, we consider the functionals over the cotangent bundle of the superloop space over a smooth manifold. We present a number of examples of the Courant-like brackets arising from this analysis.Comment: 20 pages, the version published in JHE

Dressing Technique for Intermediate Hierarchies

A generalized AKNS systems introduced and discussed recently in \cite{dGHM} are considered. It was shown that the dressing technique both in matrix pseudo-differential operators and formal series with respect to the spectral parameter can be developed for these hierarchies.Comment: 16 pages, LaTeX Report/no: DFTUZ/94/2