Cherenkov Telescope Array: The next-generation ground-based gamma-ray observatory

High energy gamma-ray astronomy is a newly emerging and very successful branch of astronomy and astrophysics. Exciting results have been obtained by the current generation Cherenkov telescope systems such as H.E.S.S., MAGIC, VERITAS and CANGAROO. The H.E.S.S. survey of the galactic plane has revealed a large number of sources and addresses issues such as the question about the origin of cosmic rays. The detection of very high energy emission from extragalactic sources at large distances has provided insights in the star formation during the history of the universe and in the understanding of active galactic nuclei. The development of the very large Cherenkov telescope array system (CTA) with a sensitivity about an order of magnitude better than current instruments and significantly improved sensitivity is under intense discussion. This observatory will reveal an order of magnitude more sources and due to its higher sensitivity and angular resolution it will be able to detect new classes of objects and phenomena that have not been visible until now. A combination of different telescope types will provide the sensitivity needed in different energy ranges.Comment: 4 pages, 3 figures, to appear in the proceedings of the 30th International Cosmic Ray Conference, Merida, July 200

Mode-coupling theory for structural and conformational dynamics of polymer melts

A mode-coupling theory for dense polymeric systems is developed which unifyingly incorporates the segmental cage effect relevant for structural slowing down and polymer chain conformational degrees of freedom. An ideal glass transition of polymer melts is predicted which becomes molecular-weight independent for large molecules. The theory provides a microscopic justification for the use of the Rouse theory in polymer melts, and the results for Rouse-mode correlators and mean-squared displacements are in good agreement with computer simulation results.Comment: 4 pages, 3 figures, Phys. Rev. Lett. in pres

Orbits in the H2O molecule

We study the forms of the orbits in a symmetric configuration of a realistic model of the H2O molecule with particular emphasis on the periodic orbits. We use an appropriate Poincar\'e surface of section (PSS) and study the distribution of the orbits on this PSS for various energies. We find both ordered and chaotic orbits. The proportion of ordered orbits is almost 100% for small energies, but decreases abruptly beyond a critical energy. When the energy exceeds the escape energy there are still non-escaping orbits around stable periodic orbits. We study in detail the forms of the various periodic orbits, and their connections, by providing appropriate stability and bifurcation diagrams.Comment: 21 pages, 14 figures, accepted for publication in CHAO

The Luminosity Functions of Old and Intermediate-Age Globular Clusters in NGC 3610

The WFPC2 Camera on board HST has been used to obtain high-resolution images of NGC 3610, a dynamically young elliptical galaxy. These observations supersede shorter, undithered HST observations where an intermediate-age population of globular clusters was first discovered. The new observations show the bimodal color distribution of globular clusters more clearly, with peaks at (V-I)o = 0.95 and 1.17. The luminosity function (LF) of the blue, metal-poor population of clusters in NGC 3610 turns over, consistent with a Gaussian distribution with a peak Mv ~= -7.0, similar to old globular-cluster populations in ellipticals. The red, metal-rich population of clusters has a LF that is more extended toward both the bright and faint ends, as expected for a cluster population of inter-mediate age. It is well fit by a power law with an exponent of alpha = -1.78 +-0.05, or -1.90+-0.07 when corrected for observational scatter. A Kolmogorov-Smirnov test confirms the significant difference between the LFs of the red and blue clusters, with a probability of less than 0.1% that they come from the same population. A comparison with the Fall & Zhang cluster disruption models shows marginal agreement with the observed LF, although there are differences in detail. In particular, there is no clear evidence of the predicted turnover at the faint end. A by-product of the analysis is the demonstration that, at any given metallicity, the peak of the LF should remain nearly constant from 1.5 Gyr to 12 Gyr, since the effect of the disruption of faint clusters is almost perfectly balanced by the fading of the clusters. This may help explain the apparent universality of the peak of the globular cluster luminosity function. (Abridged)Comment: 32 pages, LaTeX, 13 PS figures, 1 table; to appear in AJ (July 2002