5,631 research outputs found
Evidence for an intermediate line region in AGN's inner torus region and its evolution from narrow to broad line Seyfert I galaxies
A two-components model for Broad Line Region (BLR) of Active Galactic Nuclei
(AGN) has been suggested for many years but not widely accepted (e.g., Hu et
al. 2008; Sulentic et al. 2000; Brotherton et al. 1996; Mason et al. 1996).
This model indicates that the broad line can be described with superposition of
two Gaussian components (Very Broad Gaussian Component (VBGC) and InterMediate
Gaussian Component (IMGC)) which are from two physically distinct regions;
i.e., Very Broad Line Region (VBLR) and InterMediate Line Region (IMLR). We
select a SDSS sample to further confirm this model and give detailed analysis
to the geometry, density and evolution of these two regions. Micro-lensing
result of BLR in J1131-1231 and some unexplained phenomena in Reverberation
Mapping (RM) experiment provide supportive evidence for this model. Our results
indicate that the radius obtained from the emission line RM normally
corresponds to the radius of the VBLR, and the existence of the IMGC may affect
the measurement of the black hole masses in AGNs. The deviation of NLS1s from
the M-sigma relation and the Type II AGN fraction as a function of luminosity
can be explained in this model in a coherent way. The evolution of the two
emission regions may be related to the evolutionary stages of the broad line
regions of AGNs from NLS1s to BLS1s. Based on the results presented here, a
unified picture of hierarchical evolution of black hole, dust torus and galaxy
is proposed.Comment: 58 pages, 19 figures, 1 table. Matches the published versio
Parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
Flat-spectrum radio-loud Narrow-Line Seyfert 1 galaxies (NLS1s) are a
recently discovered class of -ray emitting Active Galactic Nuclei
(AGN), that exhibit some blazar-like properties which are explained with the
presence of a relativistic jet viewed at small angles. When blazars are
observed at larger angles they appear as radio-galaxies, and we expect to
observe an analogue parent population for beamed NLS1s. However, the number of
known NLS1s with the jet viewed at large angles is not enough. Therefore, we
tried to understand the origin of this deficit. Current hypotheses about the
nature of parent sources are steep-spectrum radio-loud NLS1s, radio-quiet NLS1s
and disk-hosted radio-galaxies. To test these hypotheses we built three samples
of candidate sources plus a control sample, and calculated their black hole
mass and Eddington ratio using their optical spectra. We then performed a
Kolmogorov-Smirnov statistical test to investigate the compatibility of our
different samples with a beamed population. Our results indicate that, when the
inclination angle increases, a beamed source appears as a steep-spectrum
radio-loud NLS1, or possibly even as a disk-hosted radio-galaxy with low black
hole mass and high Eddington ratio. Further investigations, involving larger
complete samples and observations at radio frequency, are needed to understand
the incidence of disk-hosted radio-galaxies in the parent population, and to
assess whether radio-quiet NLS1s can play a role, as well.Comment: 12 pages, 6 figures, accepted for publication by Astronomy and
Astrophysic
Balmer Emission Line Profiles and the Complex Properties of Broad Line Regions in Active Galactic Nuclei
In this work we analyze a sample of AGN spectra, selected from the 6th Data
Release of the Sloan Digital Sky Survey, exploiting a generalized technique of
line profile analysis, designed to take into account the whole profiles of
their broad emission lines. We find that the line profile broadening functions
result from a complex structure, but we may be able to infer some constraints
about the role of the geometrical factor, thus improving our ability to
estimate AGN properties and their relation with the host galaxy. Our results
suggest that flattening and inclination within the structure of the Broad Line
Region (BLR) must be taken into account. We detect low inclinations of the BLR
motion plane with respect to our line of sight, typically i < 20 degrees, with
a geometrical effect which generally decreases as the line profile becomes
broader.Comment: 13 pages, 11 figures, updated reference list. ApJ accepte
Compact steep-spectrum sources as the parent population of flat-spectrum radio-loud NLS1s
Narrow-line Seyfert 1 galaxies (NLS1s) are an interesting subclass of active
galactic nuclei (AGN), which tipically does not exhibit any strong radio
emission. Seven percent of them, though, are radio-loud and often show a flat
radio-spectrum (F-NLS1s). This, along to the detection of -ray emission
coming from them, is usually interpreted as a sign of a relativistic beamed jet
oriented along the line of sight. An important aspect of these AGN that must be
understood is the nature of their parent population, in other words how do they
appear when observed under different angles. In the recent literature it has
been proposed that a specific class of radio-galaxies, compact-steep sources
(CSS) classified as high excitation radio galaxies (HERG), can represent the
parent population of F-NLS1s. To test this hypothesis in a quantitative way,in
this paper we analyzed the only two statistically complete samples of CSS/HERGs
and F-NLS1s available in the literature. We derived the black hole mass and
Eddington ratio distributions, and we built for the first time the radio
luminosity function of F-NLS1s. Finally, we applied a relativistic beaming
model to the luminosity function of CSS/HERGs, and compared the result with the
observed function of F-NLS1s. We found that compact steep-spectrum sources are
valid parent candidates and that F-NLS1s, when observed with a different
inclination, might actually appear as CSS/HERGs.Comment: 9 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysic
Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite
ABSTRACT: Yeelimite, Ca4[Al6O12]SO4, is outstanding as an aluminate
sodalite, being the framework of these type of materials flexible and dependent
on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also
important from an applied perspective as it is the most important phase in
calcium sulfoaluminate cements. However, its crystal structure is not well
studied. Here, we characterize the room temperature crystal structure of
stoichiometric yeelimite through joint Rietveld refinement using neutron and Xray
powder diffraction data coupled with chemical soft-constraints. Our structural
study shows that yeelimite has a lower symmetry than that of the previously
reported tetragonal system, which we establish to likely be the acentric
orthorhombic space group Pcc2, with a â2a Ă â2a Ă a superstructure based on
the cubic sodalite structure. Final unit cell values were a = 13.0356(7) Ă
, b =
13.0350(7) Ă
, and c = 9.1677(2) Ă
. We determine several structures using
density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result.
Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 °C by
thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure,
as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our
theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group I43m. Finally, we show that
our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate
cements, as shown by RF values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the
one reported in this study, respectively.Universidad de MĂĄlaga. Campus de Excelencia Internacional. AndalucĂa Tech
Sympathy for the environment predicts green consumerism but not more important environmental behaviours related to domestic energy use
SUMMARY Household consumption is a major contributor to global greenhouse gas emissions. Some behaviours (for example energy use and vehicle use) may have far larger impacts than others (for example green consumerism of household products). Here, the driving forces of green consumerism and two domestic energy uses (electricity consumption and vehicle fuel use) are compared. This study found that environmental attitudes predicted green consumerism, but not electricity consumption or vehicle fuel use. Furthermore, green consumerism was correlated with income and individual level demographic factors, while energy consumption was primarily predicted by household size and structural constraints. Because household energy consumption has greater environmental impacts than green consumerism, policies that aim to improve pro-environmental attitudes may not be effective in mitigating greenhouse gas emissions. Policies should rather aim to change structural constraints influencing transportation and household energy decisions and improve the conspicuousness of household energy consumption
Elastic lever arm model for myosin V
We present a mechanochemical model for myosin V, a two-headed processive
motor protein. We derive the properties of a dimer from those of an individual
head, which we model both with a 4-state cycle (detached, attached with ADP.Pi,
attached with ADP and attached without nucleotide) and alternatively with a
5-state cycle (where the power stroke is not tightly coupled to the phosphate
release). In each state the lever arm leaves the head at a different, but
fixed, angle. The lever arm itself is described as an elastic rod. The chemical
cycles of both heads are coordinated exclusively by the mechanical connection
between the two lever arms. The model explains head coordination by showing
that the lead head only binds to actin after the power stroke in the trail head
and that it only undergoes its power stroke after the trail head unbinds from
actin. Both models (4- and 5-state) reproduce the observed hand-over-hand
motion and fit the measured force-velocity relations. The main difference
between the two models concerns the load dependence of the run length, which is
much weaker in the 5-state model. We show how systematic processivity
measurement under varying conditions could be used to distinguish between both
models and to determine the kinetic parameters.Comment: 15 pages, 15 figures, to appear in Biophys.
Exploring the parent population of beamed NLS1s: from the black hole to the jet
The aim of this work is to understand the nature of the parent population of
beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical
properties of three parent candidates samples: steep-spectrum radio-loud NLS1s,
radio-quiet NLS1s and disk-hosted radio-galaxies. In particular, we focused on
the black hole mass and Eddington ratio distribution and on the interactions
between the jet and the narrow-line region.Comment: 6 pages, 2 figures, to appear in Proceedings of High Energy Phenomena
in Relativistic Outflows (HEPRO) V, Workshop Series of the Argentinian
Astronomical Societ
Chemical Recycling of a Textile Blend from Polyester and Viscose, Part II: Mechanism and Reactivity during Alkaline Hydrolysis of Textile Polyester
Chemical recycling of textiles holds the potential to yield materials of equal quality and value as products from virgin feedstock. Selective depolymerization of textile polyester (PET) from regenerated cellulose/PET blends, by means of alkaline hydrolysis, renders the monomers of PET while cellulose remains in fiber form. Here, we present the mechanism and reactivity of textile PET during alkaline hydrolysis. Part I of this article series focuses on the cellulose part and a possible industrialization of such a process. The kinetics and reaction mechanism for alkaline hydrolysis of polyester packaging materials or virgin bulk polyester are well described in the scientific literature; however, information on depolymerization of PET from textiles is sparse. We find that the reaction rate of hydrolysis is not affected by disintegrating the fabric to increase its surface area. We ascribe this to the yarn structure, where texturing and a low density assures a high accessibility even without disintegration. The reaction, similar to bulk polyester, is shown to be surface specific and proceeds via endwise peeling. Finally, we show that the reaction product terephthalic acid is pure and obtained in high yields
Unveiling the parent population of beamed narrow-line Seyfert 1s
Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN)
recently identified as a new class of -ray sources. The high energy
emission is explained by the presence of a relativistic jet observed at small
angles, just like in the case of blazars. When the latter are observed at
larger angles they appear as radio-galaxies, but an analogue parent population
for beamed NLS1s has not yet been determined. In this work we analyze this
problem by studying the physical properties of three different samples of
parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s,
and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In
our approach, we first derived black hole mass and Eddington ratio from the
optical spectra, then we investigated the interaction between the jet and the
narrow-line region from the [O III] 4959,5007 lines. Finally,
the radio luminosity function allowed us to compare their jet luminosity and
hence determine the relations between the samples.Comment: 6 pages, no figures. Proceedings of the 28th Texas Symposium, Geneva,
December 13-18, 201
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