23,662 research outputs found
Metallicity of high stellar mass galaxies with signs of merger events
We focus on an analysis of galaxies of high stellar mass and low metallicity.
We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital
Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high
resolution imaging and both spectroscopic and photometric information available
in the SDSS database. For each galaxy in our sample, we conducted a systematic
morphological analysis by visual inspection of MGC images using their
luminosity contours. The galaxies are classified as either disturbed or
undisturbed objects. We divide the sample into three metallicity regions,
within wich we compare the properties of disturbed and undisturbed objects. We
find that the fraction of galaxies that are strongly disturbed, indicative of
being merger remnants, is higher when lower metallicity objects are considered.
The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed
galaxies (for high, medium, and low metallicity, respectively). Moreover, the
ratio of the disturbed to undisturbed relative distributions of the population
age indicator, Dn(4000), in the low metallicity bin, indicates that the
disturbed objects have substantially younger stellar populations than their
undisturbed counterparts. In addition, we find that an analysis of colour
distributions provides similar results, showing that low metallicity galaxies
with a disturbed morphology are bluer than those that are undisturbed. The
bluer colours and younger populations of the low metallicity, morphologically
disturbed objects suggest that they have experienced a recent merger with an
associated enhanced star formation rate. [abridged]Comment: Astronomy & Astrophysics, in pres
The multicomponent 2D Toda hierarchy: Discrete flows and string equations
The multicomponent 2D Toda hierarchy is analyzed through a factorization
problem associated to an infinite-dimensional group. A new set of discrete
flows is considered and the corresponding Lax and Zakharov--Shabat equations
are characterized. Reductions of block Toeplitz and Hankel bi-infinite matrix
types are proposed and studied. Orlov--Schulman operators, string equations and
additional symmetries (discrete and continuous) are considered. The
continuous-discrete Lax equations are shown to be equivalent to a factorization
problem as well as to a set of string equations. A congruence method to derive
site independent equations is presented and used to derive equations in the
discrete multicomponent KP sector (and also for its modification) of the theory
as well as dispersive Whitham equations.Comment: 27 pages. In the revised paper we improved the presentatio
Magnetic long-range order induced by quantum relaxation in single-molecule magnets
Can magnetic interactions between single-molecule magnets (SMMs) in a crystal
establish long-range magnetic order at low temperatures deep in the quantum
regime, where the only electron spin-fluctuations are due to incoherent
magnetic quantum tunneling (MQT)? Put inversely: can MQT provide the
temperature dependent fluctuations needed to destroy the ordered state above
some finite Tc, although it should basically itself be a T-independent process?
Our experiments on two novel Mn4 SMMs provide a positive answer to the above,
showing at the same time that MQT in the SMMs has to involve spin-lattice
coupling at a relaxation rate equaling that predicted and observed recently for
nuclear spin-mediated quantum relaxation.Comment: 4 pages, 3 figure
FeNi-based magnetoimpedance multilayers: Tailoring of the softness by magnetic spacers
The microstructure and magnetic properties of sputtered permalloy films and FeNi(170 nm)/X/FeNi(170 nm) (X=Co, Fe, Gd, Gd-Co) sandwiches were studied. Laminating of the thick FeNi film with various spacers was done in order to control the magnetic softness of FeNi-based multilayers. In contrast to the Co and Fe spacers, Gd and Gd-Co magnetic spacers improved the softness of the FeNi/X/FeNi sandwiches. The magnetoimpedance responses were measured for [FeNi/Ti(6 nm)] 2/FeNi and [FeNi/Gd(2 nm)] 2/FeNi multilayers in a frequency range of 1-500 MHz: for all frequencies under consideration the highest magnetoimpedance variation was observed for [FeNi/Gd(2 nm)] 2/FeNi multilayers. © 2012 American Institute of Physics
An Introduction to Pervasive Interface Automata
Pervasive systems are often context-dependent, component based systems in which components expose interfaces and offer one or more services. These systems may evolve in unpredictable ways, often through component replacement. We present pervasive interface automata as a formalism for modelling components and their composition. Pervasive interface automata are based on the interface automata of Henzinger et al, with several significant differences. We expand their notion of input and output actions to combinations of input, output actions, and callable methods and method calls. Whereas interfaces automata have a refinement relation, we argue the crucial relation in pervasive systems is component replacement, which must include consideration of the services offered by a component and assumptions about the environment. We illustrate pervasive interface autmotata and component replacement with a small case study of a pervasive application for sports predictions
Integrable Deformations of Algebraic Curves
A general scheme for determining and studying integrable deformations of
algebraic curves, based on the use of Lenard relations, is presented. We
emphasize the use of several types of dynamical variables : branches, power
sums and potentials.Comment: 10 Pages, Proceedings Workshop-Nonlinear Physics: Theory and
Experiment, Gallipoli 200
Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 m variability
We present a study of galaxies showing mid-infrared variability in data taken
in the deepest Spitzer/MIPS 24 m surveys in the GOODS-South field. We
divide the dataset in epochs and subepochs to study the long-term
(months-years) and the short-term (days) variability. We use a
-statistics method to select AGN candidates with a probability
1% that the observed variability is due to statistical errors alone. We find 39
(1.7% of the parent sample) sources that show long-term variability and 55
(2.2% of the parent sample) showing short-term variability. That is, 0.03
sources arcmin for both, long-term and short-term variable
sources. After removing the expected number of false positives inherent to the
method, the estimated percentages are 1.0% and 1.4% of the parent sample for
the long-term and short-term respectively. We compare our candidates with AGN
selected in the X-ray and radio bands, and AGN candidates selected by their IR
emission. Approximately, 50% of the MIPS 24 m variable sources would be
identified as AGN with these other methods. Therefore, MIPS 24 m
variability is a new method to identify AGN candidates, possibly dust obscured
and low luminosity AGN, that might be missed by other methods. However, the
contribution of the MIPS 24 m variable identified AGN to the general AGN
population is small ( 13%) in GOODS-South.Comment: Accepted for publication in MNRA
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