5,752 research outputs found
Invariant NKT cells and rheumatic disease: Focus on primary sjogren syndrome
Primary Sjogren syndrome (pSS) is a complex autoimmune disease mainly affecting salivary and lacrimal glands. Several factors contribute to pSS pathogenesis; in particular, innate immunity seems to play a key role in disease etiology. Invariant natural killer (NK) T cells (iNKT) are a T-cell subset able to recognize glycolipid antigens. Their function remains unclear, but studies have pointed out their ability to modulate the immune system through the promotion of specific cytokine milieu. In this review, we discussed the possible role of iNKT in pSS development, as well as their implications as future markers of disease activity
New insights into the structure of early-type galaxies: the Photometric Plane at z~0.3
We study the Photometric Plane (PHP), namely the relation between the
effective radius re, the mean surface brightness within that radius e, and
the Sersic index n, in optical (R and I) and near-infrared (K) bands for a
large sample of early-type galaxies (ETGs) in the rich cluster MS1008-1224 at
z=0.306. The PHP relation has an intrinsic dispersion of ~32% in re, and turns
out to be independent of waveband. This result is consistent with the fact that
internal colour gradients of ETGs can have only a mild dependence on galaxy
luminosity (mass). There is no evidence for a significant curvature in the PHP.
We show that this can be explained if this relation origins from a systematic
variation of the specific entropy of ETGs along the galaxy sequence, as was
suggested from previous works. The intrinsic scatter of the PHP is
significantly smaller than for other purely photometric relations, such as the
Kormendy relation and the photometric Fundamental Plane, which is constructed
by using colours in place of velocity dispersions. The scatter does not depend
on the waveband and the residuals about the plane do not correlate with
residuals of the colour-magnitude relation. Finally, we compare the
coefficients of the PHP at z~0.3 with those of ETGs at z~0, showing that the
PHP is a valuable tool to constrain the luminosity evolution of ETGs with
redshift. The slopes of the PHP do not change significantly with redshift,
while the zero-point is consistent with cosmological dimming of the surface
brightness in an expanding universe plus the passive fading of galaxy stellar
populations with a high formation redshift (z_f >1-2).Comment: 21 pages, 10 figures, MNRAS in pres
Global Properties of the Rich Cluster ABCG 209 at z~0.2. Spectroscopic and Photometric Catalogue
This paper is aimed at giving an overview of the global properties of the
rich cluster of galaxies ABCG 209. This is achieved by complementing the
already available data with new medium resolution spectroscopy and NIR
photometry which allow us to i) analyse in detail the cluster dynamics,
distinguishing among galaxies belonging to different substructures and deriving
their individual velocity distributions, using a total sample of 148 galaxies
in the cluster region, of which 134 belonging to the cluster; ii) derive the
cluster NIR luminosity function; iii) study the Kormendy relation and the
photometric plane of cluster early-type galaxies (ETGs). Finally we provide an
extensive photometric (optical and NIR) and spectroscopic dataset for such a
complex system to be used in further analyses investigating the nature,
formation and evolution of rich clusters of galaxies. The observational
scenario confirms that ABCG 209 is presently undergoing strong dynamical
evolution with the merging of two or more subclumps. This interpretation is
also supported by the detection of a radio halo (Giovannini et al. 2006)
suggesting that there is a recent or ongoing merging. Cluster ETGs follow a
Kormendy relation whose slope is consistent with previous studies both at
optical and NIR wavelengths. We investigate the origin of the intrinsic scatter
of the photometric plane due to trends of stellar populations, using line
indices as indicators of age, metallicity and alpha/Fe enhancement. We find
that the chemical evolution of galaxies could be responsible for the intrinsic
dispersion of the Photometric Plane.Comment: 39 pages, 17 figures, MNRAS in pres
SPIDER - IV. Optical and NIR color gradients in Early-type galaxies: New Insights into Correlations with Galaxy Properties
We present an analysis of stellar population gradients in 4,546 Early-Type
Galaxies with photometry in along with optical spectroscopy. A new
approach is described which utilizes color information to constrain age and
metallicity gradients. Defining an effective color gradient, ,
which incorporates all of the available color indices, we investigate how
varies with galaxy mass proxies, i.e. velocity dispersion,
stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and
alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age
gradients and decreasing metallicity gradients wrt mass, metallicity, and
enhancement. We find that velocity dispersion and alpha/Fe are the main drivers
of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10
M_odot, show no correlation of age, metallicity, and color gradients wrt mass,
although color gradients still correlate with stellar population parameters,
and these correlations are independent of each other. In both mass regimes, the
striking anti-correlation between color gradient and alpha-enhancement is
significant at \sim 4sigma, and results from the fact that metallicity gradient
decreases with alpha/Fe. This anti-correlation may reflect the fact that star
formation and metallicity enrichment are regulated by the interplay between the
energy input from supernovae, and the temperature and pressure of the hot X-ray
gas in ETGs. For all mass ranges, positive age gradients are associated with
old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at
low-mass, the age gradient tends to be anti-correlated with the Age parameter,
with more positive gradients at younger ages.Comment: Accepted for Publication in the Astronomical Journa
Probing galaxy evolution through the internal colour gradients, the Kormendy relations and the Photometric Plane of cluster galaxies at z~0.2
We present a detailed analysis of the photometric properties of galaxies in
the cluster \A2163B at redshift z~0.2. R-, I- and K-band structural parameters,
(half light radius r_e, mean surface brightness _e within r_e and Sersic
index n) are derived for N~60 galaxies, and are used to study their internal
colour gradients. For the first time, we use the slopes of optical-NIR Kormendy
relations to study colour gradients as a function of galaxy size, and we derive
the Photometric Plane at z~0.2 in the K band. Colour gradients are negligible
at optical wavelengths, and are negative in the optical-NIR, implying a
metallicity gradient in galaxies of ~0.2 dex per radial decade. The analysis of
the Kormendy relation suggests that its slope increases from the optical to the
NIR, implying that colour gradients do not vary or even do become less steep in
more massive galaxies. Such a result is not simply accomodated within a
monolithic collapse scenario, while it can be well understood within a
hierarchical merging framework. Finally, we derive the first NIR Photometric
Plane at z~0.2, accounting for both the correlations on the measurement
uncertainties and the selection effects. The Photometric Plane at z~0.2 is
consistent with that at z~0, with an intrinsic scatter significantly smaller
than the Kormendy relation but larger than the Fundamental Plane.Comment: 18 pages, 12 figures, A&A in pres
A hyperbolic model for the effects of urbanization on air pollution
AbstractA hyperbolic model to study effects of industrialization and urbanization on air pollution propagation is proposed.The existence of smooth and discontinuous traveling wave-like solutions, related to the spread of both the pollution in the atmosphere and the level of urbanization, is discussed. Validation of the model in point is also accomplished by searching for numerical solutions of the system of PDEs
Functionalized carbon black for elastomer composites with low hysteresis
The prime application of elastomeric composites is tire compounds. The tuning of
dynamic rigidity and hysteresis is key to achieve the desired tire performances. Car
tires require hysteresis to be high at low temperatures, to promote wet traction, and
low at medium-high temperatures, for low energy dissipations. To achieve these
properties amorphous precipitated silica is commonly selected as reinforcing filler due
to its nano dimensions and the possibility of establishing chemical bonds with the
elastomers’ chains. Carbon black (CB), another common filler for tire compounds, does
not have functional groups able to promote chemical bonds with the rubber matrix yet
it would be highly desirable. A CB with a cradle to gate LCA comparable if not even
better than silica’s LCA could be used in replacement of silica in tire compounds.
In this work, a pyrrole compound (PyC) containing a thiol group was used to
functionalize CB by the so-called “pyrrole methodology” . The thiol group was
expected to react with the sulphur-based crosslinking system, thus forming chemical
bonds with the rubber chains. The synthesis of the PyC and the functionalization
reaction were characterized by high atom efficiency. A poly(styrene-co-butadiene)
copolymer from anionic solution polymerization was used as the main rubber for the
compound preparation. The crosslinked composite material filled with functionalized
CB revealed substantial improvements with respect to the composite with pristine CB,
in particular: high rigidity and low hysteresis at high temperature. These findings seem
to confirm the formation of the expected rubber-filler chemical bond and are even
comparable to those of silica- based rubber composites. The results here reported pave
the way to CB-based rubber composites with a low environmental impact
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