386 research outputs found
Extension of the Wu-Jing equation of state (EOS) for highly porous materials: thermoelectron based theoretical model
A thermodynamic equation of state (EOS) for thermoelectrons is derived which
is appropriate for investigating the thermodynamic variations along isobaric
paths. By using this EOS and the Wu-Jing (W-J) model, an extended Hugoniot EOS
model is developed which can predict the compression behavior of highly porous
materials. Theoretical relationships for the shock temperature, bulk sound
velocity, and the isentrope are developed. This method has the advantage of
being able to model the behavior of porous metals over the full range of
applicability of pressure and porosity, whereas methods proposed in the past
have been limited in their applicability.Comment: 18 pages, 1 figure, appeared at J. Appl. Phys. 92, 5924 (2002
Systematic variation of central mass density slope in early-type galaxies
We study the total density distribution in the central regions (
effective radius, ) of early-type galaxies (ETGs), using data from
the SPIDER survey. We model each galaxy with two components (dark matter halo +
stars), exploring different assumptions for the dark matter (DM) halo profile,
and leaving stellar mass-to-light () ratios as free fitting
parameters to the data. For a Navarro et al. (1996) profile, the slope of the
total mass profile is non-universal. For the most massive and largest ETGs, the
profile is isothermal in the central regions (), while for
the low-mass and smallest systems, the profile is steeper than isothermal, with
slopes similar to those for a constant-M/L profile. For a concentration-mass
relation steeper than that expected from simulations, the correlation of
density slope with mass tends to flatten. Our results clearly point to a
"non-homology" in the total mass distribution of ETGs, which simulations of
galaxy formation suggest may be related to a varying role of dissipation with
galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
The Molecular Gas Content of z<0.1 Radio Galaxies: Linking the AGN Accretion Mode to Host Galaxy Properties
One of the main achievements in modern cosmology is the so-called `unified
model', which successfully describes most classes of active galactic nuclei
(AGN) within a single physical scheme. However, there is a particular class of
radio-luminous AGN that presently cannot be explained within this framework --
the `low-excitation' radio AGN (LERAGN). Recently, a scenario has been put
forward which predicts that LERAGN, and their regular `high-excitation' radio
AGN (HERAGN) counterparts represent different (red sequence vs. green valley)
phases of galaxy evolution. These different evolutionary states are also
expected to be reflected in their host galaxy properties, in particular their
cold gas content. To test this, here we present CO(1-0) observations toward a
sample of 11 of these systems conducted with CARMA. Combining our observations
with literature data, we derive molecular gas masses (or upper limits) for a
complete, representative, sample of 21 z<0.1 radio AGN. Our results yield that
HERAGN on average have a factor of ~7 higher gas masses than LERAGN. We also
infer younger stellar ages, lower stellar, halo, and central supermassive black
masses, as well as higher black hole accretion efficiencies in HERAGN relative
to LERAGN. These findings support the idea that high- and low-excitation radio
AGN form two physically distinct populations of galaxies that reflect different
stages of massive galaxy build-up.Comment: 8 pages, 4 figures, 4 tables; accepted for publication in Ap
High precision spectra at large redshift for dynamical DE cosmologies
The next generation mass probes will investigate DE nature by measuring
non-linear power spectra at various z, and comparing them with high precision
simulations. Producing a complete set of them, taking into account baryon
physics and for any DE state equation w(z), would really be numerically
expensive. Regularities reducing such duty are essential. This paper presents
further n-body tests of a relation we found, linking models with DE state
parameter w(z) to const.-w models, and also tests the relation in hydro
simulations.Comment: PASCOS 2010, the 16th International Symposium on Particles, Strings
and Cosmology, Valencia (Spain), July 19th - 23rd, 201
The Origin and Evolution of Fast and Slow Rotators in the Illustris Simulation
Using the Illustris simulation, we follow thousands of elliptical galaxies back in time to identify how the dichotomy between fast and slow rotating ellipticals (FRs and SRs) develops. Comparing to the survey, we show that Illustris reproduces similar elliptical galaxy rotation properties, quantified by the degree of ordered rotation, . There is a clear segregation between low-mass (), which are mostly SRs, in agreement with observations. We find that SRs are very gas poor, metal rich and red in colour, while FRs are generally more gas rich and still star forming. We suggest that ellipticals begin naturally as FRs and, as they grow in mass, lose their spin and become SRs. While at , the progenitors of SRs and FRs are nearly indistinguishable, their merger and star formation histories differ thereafter. We find that major mergers tend to disrupt galaxy spin, though in rare cases can lead to a spin-up. No major difference is found between the effects of gas-rich and gas-poor mergers and the amount of minor mergers seem to have little correlation with galaxy spin. In between major mergers, lower-mass ellipticals, which are mostly gas-rich, tend to recover their spin by accreting gas and stars. For galaxies with above , this trend reverses; galaxies only retain or steadily lose their spin. More frequent mergers, accompanied by an inability to regain spin, lead massive ellipticals to lose most of ordered rotation and transition from FRs to SRs.BPM acknowledges support from the Kavli Foundation and the German Science Foundation (DFG) for an Emmy Noether grant. The Flatiron Institute is supported by the Simons Foundation. DS acknowledges support by the STFC and the ERC Starting Grant 638707 âBlack holes and their host galaxies: co-evolution across cosmic timeâ
Orbital Cellulitis Following Uncomplicated Glaucoma Drainage Device Surgery: Case Report and Review of Literature
Purpose: Orbital cellulitis (OC) is a rare postoperative complication of glaucoma drainage device (GDD) implantation. To date, there have only been 10 reported cases of OC following GDD implantation.
Case Report: Here, we report a case of OC in a 57-year-old man who developed pain, proptosis, and limited extraocular motility two days after uneventful Ahmed FP7 implantation in the right eye. Contrast-enhanced computed tomography of the orbits demonstrated fat stranding and a small fluid collection, consistent with OC. He had minimal improvement with intravenous antibiotics and ultimately underwent GDD explantation. A systematic review of the literature showed that the development of OC following GDD implantation can occur in the early or late postoperative period. Immediate hospitalization with intravenous administration of broad-spectrum antibiotics is recommended. Explantation of the infected GDD is often required for source control.
Conclusion: OC is a rare postoperative complication of GDD implantation. Prompt evaluation and treatment are required, often combined with GDD explantation
Galactic star formation and accretion histories from matching galaxies to dark matter haloes
We present a new statistical method to determine the relationship between the
stellar masses of galaxies and the masses of their host dark matter haloes over
the entire cosmic history from z~4 to the present. This multi-epoch abundance
matching (MEAM) model self-consistently takes into account that satellite
galaxies first become satellites at times earlier than they are observed. We
employ a redshift-dependent parameterization of the stellar-to-halo mass
relation to populate haloes and subhaloes in the Millennium simulations with
galaxies, requiring that the observed stellar mass functions at several
redshifts be reproduced simultaneously. Using merger trees extracted from the
dark matter simulations in combination with MEAM, we predict the average
assembly histories of galaxies, separating into star formation within the
galaxies (in-situ) and accretion of stars (ex-situ). The peak star formation
efficiency decreases with redshift from 23% at z=0 to 9% at z=4 while the
corresponding halo mass increases from 10^11.8M\odot to 10^12.5M\odot. The star
formation rate of central galaxies peaks at a redshift which depends on halo
mass; for massive haloes this peak is at early cosmic times while for low-mass
galaxies the peak has not been reached yet. In haloes similar to that of the
Milky-Way about half of the central stellar mass is assembled after z=0.7. In
low-mass haloes, the accretion of satellites contributes little to the assembly
of their central galaxies, while in massive haloes more than half of the
central stellar mass is formed ex-situ with significant accretion of satellites
at z<2. We find that our method implies a cosmic star formation history and an
evolution of specific star formation rates which are consistent with those
inferred directly. We present convenient fitting functions for stellar masses,
star formation rates, and accretion rates as functions of halo mass and
redshift.Comment: 20 pages, 12 figures, 1 table, submitted to MNRA
Shallow Dark Matter Cusps in Galaxy Clusters
We study the evolution of the stellar and dark matter components in a galaxy
cluster of from to the present epoch using
the high-resolution collisionless simulations of Ruszkowski & Springel (2009).
At the dominant progenitor halos were populated with spherical model
galaxies with and without accounting for adiabatic contraction. We apply a
weighting scheme which allows us to change the relative amount of dark and
stellar material assigned to each simulation particle in order to produce
luminous properties which agree better with abundance matching arguments and
observed bulge sizes at . This permits the study of the effect of initial
compactness on the evolution of the mass-size relation. We find that for more
compact initial stellar distributions the size of the final Brightest Cluster
Galaxy grows with mass according to , whereas for more extended
initial distributions, . Our results show that collisionless
mergers in a cosmological context can reduce the strength of inner dark matter
cusps with changes in logarithmic slope of 0.3 to 0.5 at fixed radius. Shallow
cusps such as those found recently in several strong lensing clusters thus do
not necessarily conflict with CDM, but may rather reflect on the initial
structure of the progenitor galaxies, which was shaped at high redshift by
their formation process.Comment: 8 pages, 4 figures, submitted to MNRA
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