On Hopf's Lemma and the Strong Maximum Principle

In this paper we consider Hopf's Lemma and the Strong Maximum Principle for supersolutions to a class of non elliptic equations. In particular we prove a sufficient condition for the validity of Hopf's Lemma and of the Strong Maximum Principle and we give a condition which is at once necessary for the validity of Hopf's Lemma and sufficient for the validity of the Strong Maximum Principle.Comment: 27 pages,4 figure

How do galactic winds affect the Lyalpha forest?

We investigate the effect of galactic winds on the Lyalpha forest in cosmological simulations of structure and galaxy formation. We combine high resolution N-body simulations of the evolution of the dark matter with a semi-analytic model for the formation and evolution of galaxies which includes detailed prescriptions for the long-term evolution of galactic winds. This model is the first to describe the evolution of outflows as a two-phase process (an adiabatic bubble followed by a momentum--driven shell) and to include metal--dependent cooling of the outflowing material. We find that the main statistical properties of the Lyalpha forest, namely the flux power spectrum P(k) and the flux probability distribution function (PDF), are not significantly affected by winds and so do not significantly constrain wind models. Winds around galaxies do, however, produce detectable signatures in the forest, in particular, increased flux transmissivity inside hot bubbles, and narrow, saturated absorption lines caused by dense cooled shells. We find that the Lyalpha flux transmissivity is highly enhanced near strongly wind-blowing galaxies, almost half of all high-redshift galaxies in our sample, in agreement with the results of Adelberger et al. (2005). Finally, we propose a new method to identify absorption lines potentially due to wind shells in the Lyalpha forest: we calculate the abundance of saturated regions in spectra as a function of region width and we find that the number with widths smaller than about 1 Angstrom at z=3 and 0.6 Angstrom at z=2 may be more than doubled. This should be detectable in real spectra.Comment: 14 pages, 11 figures. Minor changes in the text. Accepted for publication in MNRA

Anisotropy probe of galactic and extra-galactic Dark Matter annihilations

We study the flux and the angular power spectrum of gamma-rays produced by Dark Matter (DM) annihilations in the Milky Way (MW) and in extra-galactic halos. The annihilation signal receives contributions from: a) the smooth MW halo, b) resolved and unresolved substructures in the MW, c) external DM halos at all redshifts, including d) their substructures. Adopting a self-consistent description of local and extra-galactic substructures, we show that the annihilation flux from substructures in the MW dominates over all the other components for angles larger than O(1) degrees from the Galactic Center, unless an extreme prescription is adopted for the substructures concentration. We also compute the angular power spectrum of gamma-ray anisotropies and find that, for an optimistic choice of the particle physics parameters, an interesting signature of DM annihilations could soon be discovered by the Fermi LAT satellite at low multipoles, l<100, where the dominant contribution comes from MW substructures with mass M>10^4 solar masses. For the substructures models we have adopted, we find that the contribution of extra-galactic annihilations is instead negligible at all scales.Comment: 14 pages, 7 figure

A critical appraisal of ATLAS9 and NextGen 5 model atmospheres

The fitting atmosphere parameters (Teff, g, and [Fe/H]) for over 300 stars in the Gunn & Striker and Jacoby et al. catalogs have been obtained relying on the Kurucz (1992) ATLAS9 and Hauschildt et al (1999) NextGen5 synthesis models. The output results are compared, and a critical appraisal of both theoretical codes is performed.Comment: 2 pages, 2 figures; proceedings of "New Quests in Stellar Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya, to be published by the Kluwer Academic Publisher

Statistical properties of the GALEX spectroscopic stellar sample

The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more than 60,000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of of stars in the range 4500<Teff<9000 K. Our preliminary results indicate that the sample is formed by a majority of main sequence F- and G-type stars, with metallicity [M/H]>-1 dex.Comment: 9 pages, 9 figures, accepted for publication in Astrophysics & Space Science, UV universe special issu

A bibliography of russian scientific and technological literature in manual control and associated areas

Manual control systems, human engineering, and man in space - bibliography of Russian literature on manned space flight technolog