6,839 research outputs found
Clustering and light profiles of galaxies in the environment of 20 Ultra Steep Spectrum Radio sources
We have analyzed galaxy properties in the neighborhood of 20 Ultra-Steep
Spectrum Radio sources (USS) taken from the WISH catalog of De Breuck et al.
(2002). Galaxies in these USS fields were identified in deep observations that
were carried out in the K'-band using the OSIRIS imager at the CTIO 4m
telescope. We find a statistically significant signal of clustering around our
sample of USS. The angular extension of the detected USS-galaxy clustering is
theta_c~20" corresponding to a spatial scale ~120 h^{-1}kpc, assuming the
sources are at z~1 in a Omega_m=0.3, Omega_{\Lambda}=0.7 model universe. These
results are in agreement with those obtained by Best (2000) for radio
galaxy-galaxy correlation, and Best et al. (2003) for radio-loud AGN-galaxy
correlation. We have also analyzed the light distribution of the galaxies by
fitting Sersic's law profiles. Our results show no significant dependence of
the galaxy shape parameters on the projected distance to the USS.Comment: Accepted for its publication in Astronomical Journal, 9 figure
Hamiltonian dynamics and constrained variational calculus: continuous and discrete settings
The aim of this paper is to study the relationship between Hamiltonian
dynamics and constrained variational calculus. We describe both using the
notion of Lagrangian submanifolds of convenient symplectic manifolds and using
the so-called Tulczyjew's triples. The results are also extended to the case of
discrete dynamics and nonholonomic mechanics. Interesting applications to
geometrical integration of Hamiltonian systems are obtained.Comment: 33 page
On the Hamilton-Jacobi Theory for Singular Lagrangian Systems
We develop a Hamilton-Jacobi theory for singular lagrangian systems using the
Gotay-Nester-Hinds constraint algorithm. The procedure works even if the system
has secondary constraints.Comment: 36 page
MS 2053.7-0449: Confirmation of a bimodal mass distribution from strong gravitational lensing
We present the first strong lensing study of the mass distribution in the
cluster MS 2053-04 based on HST archive data. This massive, X-ray luminous
cluster has a redshift z=0.583, and it is composed of two structures that are
gravitationally bound to each other. The cluster has one multiply imaged system
constituted by a double gravitational arc.
We have performed a parametric strong lensing mass reconstruction using NFW
density profiles to model the cluster potential. We also included perturbations
from 23 galaxies, modeled like elliptical singular isothermal sphere, that are
approximately within 1'x1' around the cluster center. These galaxies were
constrained in both the geometric and dynamical parameters with observational
data. Our analysis predicts a third image which is slightly demagnified. We
found a candidate for this counter-image near the expected position and with
the same F702W-F814W colors as the gravitational arcs in the cluster. The
results from the strong lensing model shows the complex structure in this
cluster, the asymmetry and the elongation in the mass distribution, and are
consistent with previous spectrophotometric results that indicate that the
cluster has a bimodal mass distribution. Finally, the derived mass profile was
used to estimate the mass within the arcs and for comparison with X-ray
estimates.Comment: To be published in ApJ (accepted
Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions
Fine management of chiral processes on solid surfaces has progressed over the
years, yet still faces the need for the controlled and selective production of
advanced chiral materials. Here, we report on the use of enantiomerically
enriched molecular building blocks to demonstrate the transmission of their
intrinsic chirality along a sequence of on-surface reactions. Triggered by
thermal annealing, the on-surface reac-tions induced in this experiment involve
firstly the coupling of the chiral reactants into chiral polymers and
subsequently their transformation into planar prochiral graphene nanoribbons.
Our study reveals that the axial chirality of the reactant is not only
transferred to the polymers, but also to the planar chirality of the graphene
nanoribbon end products. Such chirality transfer consequently allows, starting
from ad-equate enantioenriched reactants, for the controlled production of
chiral and prochiral organic nanoarchi-tectures with pre-defined handedness
Modeling benzene plume elongation mechanisms exerted by ethanol using RT3D with a general substrate interaction module
Copyright © 2008 American Geophysical Union (AGU)A mathematical model was developed to evaluate the effect of the common fuel additive ethanol on benzene fate and transport in fuel-contaminated groundwater and to discern the most influential benzene plume elongation mechanisms. The model, developed as a module for the Reactive Transport in 3 Dimensions (RT3D) model, includes commonly considered fate and transport processes (advection, dispersion, adsorption, biodegradation, and depletion of molecular oxygen during biodegradation) and substrate interactions previously not considered (e.g., a decrease in the specific benzene utilization rate due to metabolic flux dilution and/or catabolite repression) as well as microbial population shifts. Benzene plume elongation predictions, based on literature model parameters, were on the order of 40% for a constant source of E10 gasoline (10% vol/vol ethanol), which compares favorably to field observations. For low benzene concentrations (<1 mg/L), oxygen depletion during ethanol degradation was the principal mechanism hindering benzene natural attenuation. For higher benzene concentrations (exerting an oxygen demand higher than the available dissolved oxygen), metabolic flux dilution was the dominant plume elongation process. If oxygen were not limiting, as might be the case in zones undergoing aerobic biostimulation, model simulations showed that microbial growth on ethanol could offset negative substrate interactions and enhance benzene degradation, resulting in shorter plumes than baseline conditions without ethanol
Symmetries in Classical Field Theory
The multisymplectic description of Classical Field Theories is revisited,
including its relation with the presymplectic formalism on the space of Cauchy
data. Both descriptions allow us to give a complete scheme of classification of
infinitesimal symmetries, and to obtain the corresponding conservation laws.Comment: 70S05; 70H33; 55R10; 58A2
Nonholonomic constraints in -symplectic Classical Field Theories
A -symplectic framework for classical field theories subject to
nonholonomic constraints is presented. If the constrained problem is regular
one can construct a projection operator such that the solutions of the
constrained problem are obtained by projecting the solutions of the free
problem. Symmetries for the nonholonomic system are introduced and we show that
for every such symmetry, there exist a nonholonomic momentum equation. The
proposed formalism permits to introduce in a simple way many tools of
nonholonomic mechanics to nonholonomic field theories.Comment: 27 page
Social media in cardiology: Reasons to learn how to use it
Social media has changed the way we learn, educate, and interact with our peers. The dynamic nature of social media and their immediate availability through our portable devices (smartphones, tablets, smartwatches, etc.) is quickly transforming the way we participate in society. The scope of these digital tools is broad as they deal with many different aspects: Teaching and learning, case discussion, congresses coverage, peer to peer interaction, research are examples worth mentioning. The scientific societies considered more innovative, are promoting these tools between their members. These new concepts need to be known by the cardiologists to stay updated, as countless information is moving rapidly through these channels. We summarize the main reasons why learning how to use these tools to be part of the conversation is essential for the cardiologist in training or fully stablished
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