QSOs in the combined SDSS/GALEX database

We discuss selection of QSO candidates from the combined SDSS and GALEX catalogues. We discuss properties of QSOs within the combined sample, and note uncertainties in number counts and completeness, compared with other SDSS-based samples. We discuss colour and other properties with redshift within the sample and the SEDs for subsets. We estimate the numbers of faint QSOs that are classified as extended objects in the SDSS, and consequent uncertainties that follow.Comment: To appear in PAS

Galaxy Evolution in Local Group Analogs. I. A GALEX study of nearby groups

Understanding the astrophysical processes acting within galaxy groups and their effects on the evolution of the galaxy population is one of the crucial topic of modern cosmology, as almost 60% of galaxies in the Local Universe are found in groups. We imaged in the far (FUV 1539 A) and near ultraviolet (NUV 2316 A) with GALEX three nearby groups, namely LGG93, LGG127 and LGG225. We obtained the UV galaxy surface photometry and, for LGG225, the only group covered by the SDSS, the photometry in u, g, r, i, z bands. We discuss galaxy morphologies looking for interaction signatures and we analyze the SED of galaxies to infer their luminosity-weighted ages. The UV and optical photometry was also used to perform a kinematical and dynamical analysis of each group and to evaluate the stellar mass. A few member galaxies in LGG225 show a distorted UV morphology due to ongoing interactions. (FUV-NUV) colors suggest that spirals in LGG93 and LGG225 host stellar populations in their outskirts younger than that of M31 and M33 in the LG or with less extinction. The irregular interacting galaxy NGC3447A has a significantly younger stellar population (few Myr old) than the average of the other irregular galaxies in LGG225 suggesting that the encounter triggered star formation. The early-type members of LGG225, NGC3457 and NGC3522, have masses of the order of a few 10^9 Mo, comparable to the Local Group ellipticals. For the most massive spiral in LGG225, we estimate a stellar mass of ~4x10$^{10}$ Mo, comparable to M33 in the LG. Ages of stellar populations range from a few to ~7 Gyr for the galaxies in LGG225. The kinematical and dynamical analysis indicates that LGG127 and LGG225 are in a pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while LGG93 is likely virialized. (Abridged)Comment: 20 pages, 13 figures, accepted for publication in Astronomy and Astrophysic

Cooperative Spectrum Sensing Using Random Matrix Theory

In this paper, using tools from asymptotic random matrix theory, a new cooperative scheme for frequency band sensing is introduced for both AWGN and fading channels. Unlike previous works in the field, the new scheme does not require the knowledge of the noise statistics or its variance and is related to the behavior of the largest and smallest eigenvalue of random matrices. Remarkably, simulations show that the asymptotic claims hold even for a small number of observations (which makes it convenient for time-varying topologies), outperforming classical energy detection techniques.Comment: Submitted to International Symposium on Wireless Pervasive Computing 200

Poisson-Lie T-plurality of three-dimensional conformally invariant sigma models II: Nondiagonal metrics and dilaton puzzle

We look for 3-dimensional Poisson-Lie dualizable sigma models that satisfy the vanishing beta-function equations with constant dilaton field. Using the Poisson-Lie T-plurality we then construct 3-dimensional sigma models that correspond to various decompositions of Drinfeld double. Models with nontrivial dilaton field may appear. It turns out that for ``traceless'' dual algebras they satisfy the vanishing beta-function equations as well. In certain cases the dilaton cannot be defined in some of the dual models. We provide an explanation why this happens and give criteria predicting when it happens.Comment: 24 pages, the published version; changes compared to v1: typos corrected, conclusions extended, added reference

Dynamics of compact homogeneous universes

A complete description of dynamics of compact locally homogeneous universes is given, which, in particular, includes explicit calculations of Teichm\"uller deformations and careful counting of dynamical degrees of freedom. We regard each of the universes as a simply connected four dimensional spacetime with identifications by the action of a discrete subgroup of the isometry group. We then reduce the identifications defined by the spacetime isometries to ones in a homogeneous section, and find a condition that such spatial identifications must satisfy. This is essential for explicit construction of compact homogenoeus universes. Some examples are demonstrated for Bianchi II, VI${}_0$, VII${}_0$, and I universal covers.Comment: 32 pages with 2 figures (LaTeX with epsf macro package

Four dimensional Lie symmetry algebras and fourth order ordinary differential equations

Realizations of four dimensional Lie algebras as vector fields in the plane are explicitly constructed. Fourth order ordinary differential equations which admit such Lie symmetry algebras are derived. The route to their integration is described.Comment: 12 page

Electron-phonon coupling in potassium-doped graphene: Angle-resolved photoemission spectroscopy

The electron-phonon coupling in potassium-doped graphene on Ir(111) is studied via the renormalization of the pi* band near the Fermi level, using angle-resolved photoemission spectroscopy. The renormalization is found to be fairly weak and almost isotropic, with a mass enhancement parameter of lambda= 0.28(6) for both the K-M and the K-G direction. These results are found to agree well with recent first principles calculations.Comment: 5 pages, 3 figure