3,814 research outputs found
Post partial nephrectomy surveillance imaging: an evidence-based approach.
To ensure the early detection of recurrent disease, all patients should undergo routine surveillance following partial nephrectomy for renal cell carcinoma. In order to optimize resource allocation and avoid unnecessary radiation exposure, the frequency and duration of surveillance should be tailored to the individual patient's risk of cancer recurrence. The evidence for surveillance after partial nephrectomy is presented reviewing the current literature on prognostic models and proposed surveillance protocols based on the timing and patterns of renal cell carcinoma recurrence. In addition, we review recent guidelines on post partial nephrectomy surveillance as well as the literature on novel imaging techniques that may aid in early disease discovery
Un hilo invisible : Un contrapunto hilvanado en el tiempo
Se propone establecer un diálogo en contrapunto entre los artistas contemporáneos Rank, BrĂtez y Larrosa, y los artistas anĂłnimos de un remoto pasado precolombino; lo que implica un reconocimiento de los elementos opuestos en esencia y en lo visible, asĂ como tambiĂ©n encontrar aquellos puntos en comĂşn que los ligan
Continuidades de algunos movimientos artĂsticos rioplatenses : Anna Rank, Marcelo Larrosa y Judith BrĂtez
En el siglo XX, se suscitaron fervientemente diversos cambios en el arte, que generaron nuevos paradigmas conceptuales y expresiones estĂ©ticas. En el RĂo de la Plata, surge a partir del retorno del Maestro JoaquĂn Torres-GarcĂa a Montevideo en 1934, una nueva manifestaciĂłn del arte, expuesta y fundamentada por Ă©l, a partir de sus mĂşltiples conferencias y publicaciones. En consecuencia, formĂł el ya mĂtico Taller Torres-GarcĂa (TTG), posteriormente denominado Escuela del Sur. En dicho Taller se formaron destacados artistas de gran calidad plástica, entre los cuales podemos nombrar a Augusto y Horacio Torres (ambos hijos del Maestro), Julio Alpuy, Francisco Matto, Anhelo Hernández, Elsa Andrada, entre otros
Cold molecular outflows in the local Universe and their feedback effect on galaxies
We study molecular outflows in a sample of 45 local galaxies, both star
forming and AGN, primarily by using CO data from the ALMA archive and from the
literature. For a subsample we also compare the molecular outflow with the
ionized and neutral atomic phases. We infer an empirical analytical function
relating the outflow rate simultaneously to the SFR, , and galaxy
stellar mass; this relation is much tighter than the relations with the
individual quantities. The outflow kinetic power shows a larger scatter than in
previous, more biased studies, spanning from 0.1 to 5 per cent of , while the momentum rate ranges from 1 to 30 times ,
indicating that these outflows can be both energy-driven, but with a broad
range of coupling efficiencies with the ISM, and radiation pressure-driven. For
about 10 per cent of the objects the outflow energetics significantly exceed
the maximum theoretical values; we interpret these as 'fossil outflows'
resulting from activity of a past strong AGN, which has now faded. We estimate
that, in the stellar mass range probed here ( 10), less
than 5 per cent of the outflowing gas escapes the galaxy. The molecular gas
depletion time associated with the outflow can be as short as a few million
years in powerful AGN, however, the total gas (H+HI) depletion times are
much longer. Altogether, our findings suggest that even AGN-driven outflows
might be relatively ineffective in clearing galaxies of their entire gas
content, although they are likely capable of clearing and quenching the central
region
Measurement of Galactic Logarithmic Spiral Arm Pitch Angle Using Two-Dimensional Fast Fourier Transform Decomposition
A logarithmic spiral is a prominent feature appearing in a majority of
observed galaxies. This feature has long been associated with the traditional
Hubble classification scheme, but historical quotes of pitch angle of spiral
galaxies have been almost exclusively qualitative. We have developed a
methodology, utilizing two-dimensional fast Fourier transformations of images
of spiral galaxies, in order to isolate and measure the pitch angles of their
spiral arms. Our technique provides a quantitative way to measure this
morphological feature. This will allow comparison of spiral galaxy pitch angle
to other galactic parameters and test spiral arm genesis theories. In this
work, we detail our image processing and analysis of spiral galaxy images and
discuss the robustness of our analysis techniques.Comment: 23 pages, 22 figures, and 3 Tables; published in ApJS 199, 33
http://iopscience.iop.org/0067-0049/199/2/33/; software available for
download at http://dafix.uark.edu/~ages/downloads.html and
http://astro.host.ualr.edu/2DFFT
Gas accretion as the origin of chemical abundance gradients in distant galaxies
It has recently been suggested that galaxies in the early Universe can grow
through the accretion of cold gas, and that this may have been the main driver
of star formation and stellar mass growth. Because the cold gas is essentially
primordial, it has a very low abundance of elements heavier than helium
(metallicity). As it is funneled to the centre of a galaxy, it will lead the
central gas having an overall lower metallicity than gas further from the
centre, because the gas further out has been enriched by supernovae and stellar
winds, and not diluted by the primordial gas. Here we report chemical
abundances across three rotationally-supported star-forming galaxies at z~3,
only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central,
star forming regions having a lower metallicity than less active ones, opposite
to what is seen in local galaxies. We conclude that the central gas has been
diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included
her
Dynamical Measurements of Black Hole Masses in Four Brightest Cluster Galaxies at 100 Mpc
We present stellar kinematics and orbit superposition models for the central
regions of four Brightest Cluster Galaxies (BCGs), based upon integral-field
spectroscopy at Gemini, Keck, and McDonald Observatories. Our integral-field
data span radii from < 100 pc to tens of kpc. We report black hole masses,
M_BH, of 2.1 +/- 1.6 x 10^10 M_Sun for NGC 4889, 9.7 + 3.0 - 2.6 x 10^9 M_Sun
for NGC 3842, and 1.3 + 0.5 - 0.4 x 10^9 M_Sun for NGC 7768. For NGC 2832 we
report an upper limit of M_BH < 9 x 10^9 M_Sun. Stellar orbits near the center
of each galaxy are tangentially biased, on comparable spatial scales to the
galaxies' photometric cores. We find possible photometric and kinematic
evidence for an eccentric torus of stars in NGC 4889, with a radius of nearly 1
kpc. We compare our measurements of M_BH to the predicted black hole masses
from various fits to the relations between M_BH and stellar velocity
dispersion, luminosity, or stellar mass. The black holes in NGC 4889 and NGC
3842 are significantly more massive than all dispersion-based predictions and
most luminosity-based predictions. The black hole in NGC 7768 is consistent
with a broader range of predictions.Comment: 24 pages, 18 figures. Accepted for publication in Ap
The Halo Occupation Distribution of Active Galactic Nuclei
Using a fully cosmological hydrodynamic simulation that self-consistently
incorporates the growth and feedback of supermassive black holes and the
physics of galaxy formation, we examine the effects of environmental factors
(e.g., local gas density, black hole feedback) on the halo occupation
distribution of low luminosity active galactic nuclei (AGN). We decompose the
mean occupation function into central and satellite contribution and compute
the conditional luminosity functions (CLF). The CLF of the central AGN follows
a log-normal distribution with the mean increasing and scatter decreasing with
increasing redshifts. We analyze the light curves of individual AGN and show
that the peak luminosity of the AGN has a tighter correlation with halo mass
compared to instantaneous luminosity. We also compute the CLF of satellite AGN
at a given central AGN luminosity. We do not see any significant correlation
between the number of satellites with the luminosity of the central AGN at a
fixed halo mass. We also show that for a sample of AGN with luminosity above
10^42 ergs/s the mean occupation function can be modeled as a softened step
function for central AGN and a power law for the satellite population. The
radial distribution of AGN inside halos follows a power law at all redshifts
with a mean index of -2.33 +/- 0.08. Incorporating the environmental dependence
of supermassive black hole accretion and feedback, our formalism provides a
theoretical tool for interpreting current and future measurements of AGN
clustering.Comment: 14 pages, 11 figures, 2 Tables (Matches the MNRAS accepted version
Formation of Supermassive Black Holes
Evidence shows that massive black holes reside in most local galaxies.
Studies have also established a number of relations between the MBH mass and
properties of the host galaxy such as bulge mass and velocity dispersion. These
results suggest that central MBHs, while much less massive than the host (~
0.1%), are linked to the evolution of galactic structure. In hierarchical
cosmologies, a single big galaxy today can be traced back to the stage when it
was split up in hundreds of smaller components. Did MBH seeds form with the
same efficiency in small proto-galaxies, or did their formation had to await
the buildup of substantial galaxies with deeper potential wells? I briefly
review here some of the physical processes that are conducive to the evolution
of the massive black hole population. I will discuss black hole formation
processes for `seed' black holes that are likely to place at early cosmic
epochs, and possible observational tests of these scenarios.Comment: To appear in The Astronomy and Astrophysics Review. The final
publication is available at http://www.springerlink.co
Treatment-Mediated Alterations in HIV Fitness Preserve CD4+ T Cell Counts but Have Minimal Effects on Viral Load
For most HIV-infected patients, antiretroviral therapy controls viral replication. However, in some patients drug resistance can cause therapy to fail. Nonetheless, continued therapy with a failing regimen can preserve or even lead to increases in CD4+ T cell counts. To understand the biological basis of these observations, we used mathematical models to explain observations made in patients with drug-resistant HIV treated with enfuvirtide (ENF/T-20), an HIV-1 fusion inhibitor. Due to resistance emergence, ENF was removed from the drug regimen, drug-sensitive virus regrown, and ENF was re-administered. We used our model to study the dynamics of plasma-viral RNA and CD4+ T cell levels, and the competition between drug-sensitive and resistant viruses during therapy interruption and re-administration. Focusing on resistant viruses carrying the V38A mutation in gp41, we found ENF-resistant virus to be 17±3% less fit than ENF-sensitive virus in the absence of the drug, and that the loss of resistant virus during therapy interruption was primarily due to this fitness cost. Using viral dynamic parameters estimated from these patients, we show that although re-administration of ENF cannot suppress viral load, it can, in the presence of resistant virus, increase CD4+ T cell counts, which should yield clinical benefits. This study provides a framework to investigate HIV and T cell dynamics in patients who develop drug resistance to other antiretroviral agents and may help to develop more effective strategies for treatment
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