422 research outputs found
Modeling the total and polarized emission in evolving galaxies: "spotty" magnetic structures
Future radio observations with the SKA and its precursors will be sensitive
to trace spiral galaxies and their magnetic field configurations up to redshift
. We suggest an evolutionary model for the magnetic configuration in
star-forming disk galaxies and simulate the magnetic field distribution, the
total and polarized synchrotron emission, and the Faraday rotation measures for
disk galaxies at z\la 3. Since details of dynamo action in young galaxies are
quite uncertain, we model the dynamo action heuristically relying only on
well-established ideas of the form and evolution of magnetic fields produced by
the mean-field dynamo in a thin disk. We assume a small-scale seed field which
is then amplified by the small-scale turbulent dynamo up to energy
equipartition with kinetic energy of turbulence. The large-scale galactic
dynamo starts from seed fields of 100 pc and an averaged regular field strength
of 0.02\,G, which then evolves to a "spotty" magnetic field configuration
in about 0.8\,Gyr with scales of about one kpc and an averaged regular field
strength of 0.6\,G. The evolution of these magnetic spots is simulated
under the influence of star formation, dynamo action, stretching by
differential rotation of the disk, and turbulent diffusion. The evolution of
the regular magnetic field in a disk of a spiral galaxy, as well as the
expected total intensity, linear polarization and Faraday rotation are
simulated in the rest frame of a galaxy at 5\,GHz and 150\,MHz and in the rest
frame of the observer at 150\,MHz. We present the corresponding maps for
several epochs after disk formation. (abridged)Comment: 13 pages, 6 figures, 2 tables, revised version is accepted for
publication in Astronomische Nachrichte
Revealing chlorinated ethene transformation hotspots in a nitrate-impacted hyporheic zone
Hyporheic zones are increasingly thought of as natural bioreactors, capable of transforming and attenuating groundwater pollutants present in diffuse baseflow. An underappreciated scenario in the understanding of contaminant fate hyporheic zones is the interaction between point-source trichloroethene (TCE) plumes and ubiquitous, non-point source pollutants such as nitrate. This study aims to conceptualise critical biogeochemical gradients in the hyporheic zone which govern the export potential of these redox-sensitive pollutants from carbon-poor, oxic aquifers. Within the TCE plume discharge zone, discrete vertical profiling of the upper 100 cm of sediment pore water chemistry revealed an 80% increase in dissolved organic carbon (DOC) concentrations and 20–60 cm thick hypoxic zones (50 mg L−1) create a large stoichiometric demand for bioavailable DOC in discharging groundwater. With the benefit of a high-resolution grid of pore water samplers investigating the shallowest 30 cm of hypoxic groundwater flow paths, we identified DOC-rich hotspots associated with submerged vegetation (Ranunculus spp.), where low-energy metabolic processes such as mineral dissolution/reduction, methanogenesis and ammonification dominate. Using a chlorine index metric, we show that enhanced TCE to cDCE transformation takes place within these biogeochemical hotspots, highlighting their relevance for natural plume attenuation
A Theoretical Interpretation of the Black Hole Fundamental Plane
We examine the origin and evolution of correlations between properties of
supermassive black holes (BHs) and their host galaxies using simulations of
major galaxy mergers, including the effects of gas dissipation, cooling, star
formation, and BH accretion and feedback. We demonstrate that the simulations
predict the existence of a BH 'fundamental plane' (BHFP), of the form M_BH
sigma^(3.0+-0.3)*R_e^(0.43+-0.19) or M_BH
M_bulge^(0.54+-0.17)*sigma^(2.2+-0.5), similar to relations found
observationally. The simulations indicate that the BHFP can be understood
roughly as a tilted intrinsic correlation between BH mass and spheroid binding
energy, or the condition for feedback coupling to power a pressure-driven
outflow. While changes in halo circular velocity, merger orbital parameters,
progenitor disk redshifts and gas fractions, ISM gas pressurization, and other
parameters can drive changes in e.g. sigma at fixed M_bulge, and therefore
changes in the M_BH-sigma or M_BH-M_bulge relations, the BHFP is robust. Given
the empirical trend of decreasing R_e for a given M_bulge at high redshift, the
BHFP predicts that BHs will be more massive at fixed M_bulge, in good agreement
with recent observations. This evolution in the structural properties of merger
remnants, to smaller R_e and larger sigma (and therefore larger M_BH,
conserving the BHFP) at a given M_bulge, is driven by the fact that bulge
progenitors have characteristically larger gas fractions at high redshifts.
Adopting the observed evolution of disk gas fractions with redshift, our
simulations predict the observed trends in both R_e(M_bulge) and M_BH(M_bulge).Comment: 22 pages, 19 figures, replaced with version accepted to ApJ.
Companion paper to arXiv:0707.400
A Halo Model with Environment Dependence: Theoretical Considerations
We present a modification of the standard halo model with the goal of
providing an improved description of galaxy clustering. Recent surveys, like
the Sloan Digital Sky Survey (SDSS) and the Anglo-Australian Two-degree survey
(2dF), have shown that there seems to be a correlation between the clustering
of galaxies and their properties such as metallicity and star formation rate,
which are believed to be environment-dependent. This environmental dependence
is not included in the standard halo model where the host halo mass is the only
variable specifying galaxy properties. In our approach, the halo properties
i.e., the concentration, and the Halo Occupation Distribution --HOD--
prescription, will not only depend on the halo mass (like in the standard halo
model) but also on the halo environment. We examine how different environmental
dependence of halo concentration and HOD prescription affect the correlation
function. We see that at the level of dark matter, the concentration of haloes
affects moderately the dark matter correlation function only at small scales.
However the galaxy correlation function is extremely sensitive to the HOD
details, even when only the HOD of a small fraction of haloes is modified.Comment: 23 pages, 17 figures. Accepted for publication in MNRA
Gravitational Quenching in Massive Galaxies and Clusters by Clumpy Accretion
We consider a simple gravitational-heating mechanism for the long-term
quenching of cooling flows and star formation in massive dark-matter haloes
hosting ellipticals and clusters. The virial shock heating in haloes >10^12 Mo
triggers quenching in 10^12-13 Mo haloes (Birnboim, Dekel & Neistein 2007). We
show that the long-term quenching in haloes >Mmin~7x10^12 Mo could be due to
the gravitational energy of cosmological accretion delivered to the inner-halo
hot gas by cold flows via ram-pressure drag and local shocks. Mmin is obtained
by comparing the gravitational power of infall into the potential well with the
overall radiative cooling rate. The heating wins if the gas inner density cusp
is not steeper than r^-0.5 and if the masses in the cold and hot phases are
comparable. The effect is stronger at higher redshifts, making the maintenance
easier also at later times. Clumps >10^5 Mo penetrate to the inner halo with
sufficient kinetic energy before they disintegrate, but they have to be <10^8
Mo for the drag to do enough work in a Hubble time. Pressure confined ~10^4K
clumps are stable against their own gravity and remain gaseous once below the
Bonnor-Ebert mass ~10^8 Mo. They are also immune to tidal disruption. Clumps in
the desired mass range could emerge by thermal instability in the outer halo if
the conductivity is not too high. Alternatively, such clumps may be embedded in
dark-matter subhaloes if the ionizing flux is ineffective, but they separate
from their subhaloes by ram pressure before entering the inner halo. Heating by
dynamical friction becomes dominant for massive satellites, which can
contribute up to one third of the total gravitational heating. We conclude that
gravitational heating by cosmological accretion is a viable alternative to AGN
feedback as a long-term quenching mechanism.Comment: 24 pages, 20 figures, some improvements, MNRAS accepted versio
Gravitational Quenching in Massive Galaxies and Clusters by Clumpy Accretion
We consider a simple gravitational-heating mechanism for the long-term
quenching of cooling flows and star formation in massive dark-matter haloes
hosting ellipticals and clusters. The virial shock heating in haloes >10^12 Mo
triggers quenching in 10^12-13 Mo haloes (Birnboim, Dekel & Neistein 2007). We
show that the long-term quenching in haloes >Mmin~7x10^12 Mo could be due to
the gravitational energy of cosmological accretion delivered to the inner-halo
hot gas by cold flows via ram-pressure drag and local shocks. Mmin is obtained
by comparing the gravitational power of infall into the potential well with the
overall radiative cooling rate. The heating wins if the gas inner density cusp
is not steeper than r^-0.5 and if the masses in the cold and hot phases are
comparable. The effect is stronger at higher redshifts, making the maintenance
easier also at later times. Clumps >10^5 Mo penetrate to the inner halo with
sufficient kinetic energy before they disintegrate, but they have to be <10^8
Mo for the drag to do enough work in a Hubble time. Pressure confined ~10^4K
clumps are stable against their own gravity and remain gaseous once below the
Bonnor-Ebert mass ~10^8 Mo. They are also immune to tidal disruption. Clumps in
the desired mass range could emerge by thermal instability in the outer halo if
the conductivity is not too high. Alternatively, such clumps may be embedded in
dark-matter subhaloes if the ionizing flux is ineffective, but they separate
from their subhaloes by ram pressure before entering the inner halo. Heating by
dynamical friction becomes dominant for massive satellites, which can
contribute up to one third of the total gravitational heating. We conclude that
gravitational heating by cosmological accretion is a viable alternative to AGN
feedback as a long-term quenching mechanism.Comment: 24 pages, 20 figures, some improvements, MNRAS accepted versio
Dynamical Mean-Field Theory and Its Applications to Real Materials
Dynamical mean-field theory (DMFT) is a non-perturbative technique for the
investigation of correlated electron systems. Its combination with the local
density approximation (LDA) has recently led to a material-specific
computational scheme for the ab initio investigation of correlated electron
materials. The set-up of this approach and its application to materials such as
(Sr,Ca)VO_3, V_2O_3, and Cerium is discussed. The calculated spectra are
compared with the spectroscopically measured electronic excitation spectra. The
surprising similarity between the spectra of the single-impurity Anderson model
and of correlated bulk materials is also addressed.Comment: 20 pages, 9 figures, invited paper for the JPSJ Special Issue "Kondo
Effect - 40 Years after the Discovery"; final version, references adde
Metastatic renal cell cancer treatments: An indirect comparison meta-analysis
Abstract
Background
Treatment for metastatic renal cell cancer (mRCC) has advanced dramatically with understanding of the pathogenesis of the disease. New treatment options may provide improved progression-free survival (PFS). We aimed to determine the relative effectiveness of new therapies in this field.
Methods
We conducted comprehensive searches of 11 electronic databases from inception to April 2008. We included randomized trials (RCTs) that evaluated bevacizumab, sorafenib, and sunitinib. Two reviewers independently extracted data, in duplicate. Our primary outcome was investigator-assessed PFS. We performed random-effects meta-analysis with a mixed treatment comparison analysis.
Results
We included 3 bevacizumab (2 of bevacizumab plus interferon-a [IFN-a]), 2 sorafenib, 1 sunitinib, and 1 temsirolimus trials (total n = 3,957). All interventions offer advantages for PFS. Using indirect comparisons with interferon-α as the common comparator, we found that sunitinib was superior to both sorafenib (HR 0.58, 95% CI, 0.38–0.86, P = < 0.001) and bevacizumab + IFN-a (HR 0.75, 95% CI, 0.60–0.93, P = 0.001). Sorafenib was not statistically different from bevacizumab +IFN-a in this same indirect comparison analysis (HR 0.77, 95% CI, 0.52–1.13, P = 0.23). Using placebo as the similar comparator, we were unable to display a significant difference between sorafenib and bevacizumab alone (HR 0.81, 95% CI, 0.58–1.12, P = 0.23). Temsirolimus provided significant PFS in patients with poor prognosis (HR 0.69, 95% CI, 0.57–0.85).
Conclusion
New interventions for mRCC offer a favourable PFS for mRCC compared to interferon-α and placebo
Constraining Running Non-Gaussianity
The primordial non-Gaussian parameter fNL has been shown to be
scale-dependent in several models of inflation with a variable speed of sound.
Starting from a simple ansatz for a scale-dependent amplitude of the primordial
curvature bispectrum for two common phenomenological models of primordial
non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the
temperature and polarization of the Cosmic Microwave Background (CMB) radiation
and derive the expected constraints on the parameter nNG that quantifies the
running of fNL(k) for current and future CMB missions such as WMAP, Planck and
CMBPol. We find that CMB information alone, in the event of a significant
detection of the non-Gaussian component, corresponding to fNL = 50 for the
local model and fNL = 100 for the equilateral model of non-Gaussianity, is able
to determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG =
0.3, respectively, for the Planck mission. In addition, we consider a Fisher
matrix analysis of the galaxy power spectrum to determine the expected
constraints on the running parameter nNG for the local model and of the galaxy
bispectrum for the equilateral model from future photometric and spectroscopic
surveys. We find that, in both cases, large-scale structure observations should
achieve results comparable to or even better than those from the CMB, while
showing some complementarity due to the different distribution of the
non-Gaussian signal over the relevant range of scales. Finally, we compare our
findings to the predictions on the amplitude and running of non-Gaussianity of
DBI inflation, showing how the constraints on a scale-dependent fNL(k)
translate into constraints on the parameter space of the theory.Comment: 37 pages, 14 figure
Morphological effects on IR band profiles: Experimental spectroscopic analysis with application to observed spectra of oxygen-rich AGB stars
To trace the source of the unique 13, 19.5, and 28 m emission features
in the spectra of oxygen-rich circumstellar shells around AGB stars, we have
compared dust extinction spectra obtained by aerosol measurements. We have
measured the extinction spectra for 19 oxide powder samples of eight different
types, such as Ti-compounds (TiO, TiO, TiO, TiO,
AlTiO, CaTiO), -, -,
---AlO, and MgAlO in the infrared region
(10 - 50 m) paying special attention to the morphological (size, shape,
and agglomeration) effects and the differences in crystal structure. Anatase
(TiO) particles with rounded edges are the possible 13, 19.5 and 28 m
band carriers as the main contributor in the spectra of AGB stars, and
spherically shaped nano-sized spinel and AlTiO dust grains are possibly
associated with the anatase, enhancing the prominence of the 13 m feature
and providing additional features at 28 m. The extinction data sets
obtained by the aerosol and CsI pellet measurements have been made available
for public use at http://elbe.astro.uni-jena.deComment: 17 pages, 8 figures, Accepted 24 March 2009 for publication in A&
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