573 research outputs found
Setting the normalcy level of HI properties in isolated galaxies
Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
Conference Serie
Size and shape of the repetitive domain of high molecular weight wheat gluten proteins. 1. Small angle neutron scattering
The solution structure of the central repetitive domain of high molecular weight (HMW) wheat gluten proteins has been investigated for a range of concentrations and temperatures using mainly small-angle neutron scattering. A representative part of the repetitive domain (dBl) was studied as well as an "oligomer" basically consisting of four dBl units, which has a length similar to the complete central domain. The scattering data over the entire angular range of both proteins are in quantitative agreement with a structural model based on a worm-like chain, a model frequently used in polymer theory. This model describes the "supersecondary, structure" of dBl and dB4 as a semiflexible cylinder with a length of about 235 and 900 Angstrom, respectively, and a cross-sectional diameter of about 15 Angstrom. The flexibility of both proteins is characterized by a persistence length of about 13 Angstrom. Their structures are thus quantitatively identical, which implies that the central HMW domain can be elongated while retaining its structural characteristics. It seems conceivable that the flexible cylinder results from a helical structure, which resembles the beta-spiral observed in earlier studies on gluten proteins and elastin. However, compared to the previously, proposed structure of a (stiff) rod, our experiments clearly indicate flexibility of the cylinder. (C) 2003 Wiley Periodicals, Inc
Kinematic modelling of disk galaxies I. A new method to fit tilted rings to data cubes
This is the first of a series of papers in which the kinematics of disk
galaxies over a range of scales is scrutinised employing spectroscopy. A
fundamental aspect of these studies is presented here: the new publicly
available software tool TiRiFiC
(http://www.astro.uni-bonn.de/~gjozsa/tirific.html) enables a direct fit of a
``tilted-ring model'' to spectroscopic data cubes. The algorithm generates
model data cubes from the tilted-ring parametrisation of a rotating disk, which
are automatically adjusted to reach an optimum fit via a chi-squared
minimisation method to an observed data cube. The structure of the new
software, the shortcomings of the previously available programs to produce a
tilted-ring model, and the performance of TiRiFiC are discussed. Our method is
less affected by the well-known problem of beam smearing that occurs when
fitting to the velocity field. Since with our method we fit many data points in
a data cube simultaneously, TiRiFiC is sensitive to very faint structures and
can hence be used to derive tilted-ring models significantly extending in
radius beyond those derived from a velocity field. The software is able to
parametrise HI disks of galaxies that are intersected by the line-of-sight
twice or more, i.e. if the disks are heavily warped, and/or with a significant
shift of the projected centre of rotation, and/or if seen edge-on. Furthermore,
our method delivers the surface-brightness profile of the examined galaxy in
addition to the orientational parameters and the rotation curve. In order to
derive kinematic and morphological models of disk galaxies, especially reliable
rotation curves, a direct-fit method as implemented in our code should be the
tool of choice.Comment: 37 pages, 24 figures. Accepted for publication in Astronomy and
Astrophysic
Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis
The generalized Chaplygin gas (GCG) model in spatially flat universe is
investigated. The cosmological consequences led by GCG model including the
evolution of EoS parameter, deceleration parameter and dimensionless Hubble
parameter are calculated. We show that the GCG model behaves as a general
quintessence model. The GCG model can also represent the pressureless CDM model
at the early time and cosmological constant model at the late time. The
dependency of transition from decelerated expansion to accelerated expansion on
the parameters of model is investigated. The statefinder parameters and
in this model are derived and the evolutionary trajectories in plane are
plotted. Finally, based on current observational data, we plot the evolutionary
trajectories in and planes for best fit values of the parameters of
GCG model. It has been shown that although, there are similarities between GCG
model and other forms of chaplygin gas in statefinder plane, but the distance
of this model from the CDM fixed point in diagram is shorter
compare with standard chaplygin gas model.Comment: 10 pages, 5 figures, accepted in Astrophys Space Sci. (2011
Aniline incorporated silica nanobubbles
We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline
molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted
emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution,
precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of
gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective
removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The
material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and
voltammetric properties of the system were studied in order to understand the interaction of aniline with
the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the
silica shell
E-/P-selectins and colon carcinoma metastasis: first in vivo evidence for their crucial role in a clinically relevant model of spontaneous metastasis formation in the lung
Entrepreneurs’ age, institutions, and social value creation goals: a multi-country study
This study explores the relationship between an entrepreneur's age and his/her social value creation goals. Building on the lifespan developmental psychology literature and institutional theory, we hypothesize a U-shaped relationship between entrepreneurs’ age and their choice to create social value through their ventures, such that younger and older entrepreneurs create more social value with their businesses while middle age entrepreneurs are relatively more economically and less socially oriented with their ventures. We further hypothesize that the quality of a country’s formal institutions in terms of economic, social, and political freedom steepen the U-shaped relationship between entrepreneurs’ age and their choice to pursue social value creation as supportive institutional environments allow entrepreneurs to follow their age-based preferences. We confirm our predictions using multilevel mixed-effects linear regressions on a sample of over 15,000 entrepreneurs (aged between 18 and 64 years) in 45 countries from Global Entrepreneurship Monitor data. The findings are robust to several alternative specifications. Based on our findings, we discuss implications for theory and practice, and we propose future research directions
The prognostic significance of tumour cell detection in the peripheral blood versus the bone marrow in 733 early-stage breast cancer patients
Colliders and Cosmology
Dark matter in variations of constrained minimal supersymmetric standard
models will be discussed. Particular attention will be given to the comparison
between accelerator and direct detection constraints.Comment: Submitted for the SUSY07 proceedings, 15 pages, LaTex, 26 eps figure
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
- …