378 research outputs found
PA6 and halloysite nanotubes composites with improved hydrothermal ageing resistance : role of filler physicochemical properties, functionalization and dispersion technique
Polyamide 6 (PA6) suffers from fast degradation in humid conditions due to hydrolysis of amide bonds, which limits its durability. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become privileged site for moisture accumulation. As a cost-effective and versatile material, halloysite nanotubes (HNT) were investigated to prepare PA6 nanocomposites with very low loadings (1-45% w/w). The roles of the physicochemical properties of two differently sourced HNT, of filler functionalization with (3-aminopropyl)triethoxysilane and of dispersion techniques (in situ polymerization vs. melt blending) were investigated. The aspect ratio (5 vs. 15) and surface charge (-31 vs.-59 mV) of the two HNT proved crucial in determining their distribution within the polymer matrix. In situ polymerization of functionalized HNT leads to enclosed and well-penetrated filler within the polymer matrix. PA6 nanocomposites crystal growth and nucleation type were studied according to Avrami theory, as well as the formation of different crystalline structures (\u3b1 and \u3b3 forms). After 1680 h of ageing, functionalized HNT reduced the diffusion of water into polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability also regarding molecular weights and rheological behavior
The predictive and prognostic potential of plasma telomerase reverse transcriptase (TERT) RNA in rectal cancer patients
Background: Preoperative chemoradiotherapy (CRT) followed by surgery is the standard care for locally advanced rectal cancer,
but tumour response to CRT and disease outcome are variable. The current study aimed to investigate the effectiveness of plasma
telomerase reverse transcriptase (TERT) levels in predicting tumour response and clinical outcome.
Methods: 176 rectal cancer patients were included. Plasma samples were collected at baseline (before CRT\ubcT0), 2 weeks after
CRT was initiated (T1), post-CRT and before surgery (T2), and 4\u20138 months after surgery (T3) time points. Plasma TERT mRNA levels
and total cell-free RNA were determined using real-time PCR.
Results: Plasma levels of TERT were significantly lower at T2 (Po0.0001) in responders than in non-responders. Post-CRT TERT
levels and the differences between pre- and post-CRT TERT levels independently predicted tumour response, and the prediction
model had an area under curve of 0.80 (95% confidence interval (CI) 0.73\u20130.87). Multiple analysis demonstrated that patients with
detectable TERT levels at T2 and T3 time points had a risk of disease progression 2.13 (95% CI 1.10\u20134.11)-fold and 4.55 (95% CI
1.48\u201313.95)-fold higher, respectively, than those with undetectable plasma TERT levels.
Conclusions: Plasma TERT levels are independent markers of tumour response and are prognostic of disease progression in rectal
cancer patients who undergo neoadjuvant therapy
Quadruple-peaked spectral line profiles as a tool to constrain gravitational potential of shell galaxies
Stellar shells observed in many giant elliptical and lenticular as well as a
few spiral and dwarf galaxies, presumably result from galaxy mergers.
Line-of-sight velocity distributions of the shells could, in principle, if
measured with a sufficiently high S/N, constitute one of methods to constrain
the gravitational potential of the host galaxy. Merrifield & Kuijken (1998)
predicted a double-peaked line profile for stationary shells resulting from a
nearly radial minor merger. In this paper, we aim at extending their analysis
to a more realistic case of expanding shells, inherent to the merging process,
whereas we assume the same type of merger and the same orbital geometry. We use
analytical approach as well as test particle simulations to predict the
line-of-sight velocity profile across the shell structure. Simulated line
profiles are convolved with spectral PSFs to estimate the peak detectability.
The resulting line-of-sight velocity distributions are more complex than
previously predicted due to non-zero phase velocity of the shells. In
principle, each of the Merrifield & Kuijken (1998) peaks splits into two,
giving a quadruple-peaked line profile, which allows more precise determination
of the potential of the host galaxy and, moreover, contains additional
information. We find simple analytical expressions that connect the positions
of the four peaks of the line profile and the mass distribution of the galaxy,
namely the circular velocity at the given shell radius and the propagation
velocity of the shell. The analytical expressions were applied to a
test-particle simulation of a radial minor merger and the potential of the
simulated host galaxy was successfully recovered. The shell kinematics can thus
become an independent tool to determine the content and distribution of the
dark matter in shell galaxies, up to ~100 kpc from the center of the host
galaxy.Comment: 15 pages, 16 figures | v2: accepted for publication in A&A, minor
language correction
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
Formation of Low Mass Stars in Elliptical Galaxy Cooling Flows
X-ray emission from hot (T = 10^7 K) interstellar gas in massive elliptical
galaxies indicates that 10^{10} M_sun has cooled over a Hubble time, but
optical and radio evidence for this cold gas is lacking. We provide detailed
theoretical support for the hypothesis that this gas has formed into low
luminosity stars. Within several kpc of the galactic center, interstellar gas
first cools to T = 10^4 K where it is heated by stellar UV and emits the
observed diffuse optical line emission. This cooling occurs at a large number
(10^6) of isolated sites. After less than a solar mass of gas has accumulated
(10^{-6} M_sun/yr) at a typical cooling site, a neutral (HI or H_2) core
develops in the HII cloud where gas temperatures drop to T = 15 K and the
ionization level (from thermal X-rays) is very low (x = 10^{-6}). We show that
the maximum mass of cores that become gravitationally unstable is only about 2
M_sun. No star can exceed this mass. Fragmentation of collapsing cores produces
a population of low mass stars with a bottom-heavy IMF and radial orbits.
Gravitational collapse and ambipolar diffusion are rapid. The total mass of
star-forming (dust-free) HI or H_2 cores in a typical bright elliptical is only
10^6 M_sun, below current observational thresholds.Comment: 23 pages in AASTEX LaTeX with 8 figures; accepted by Astrophysical
Journa
Small scale systems of galaxies I. Photometric and spectroscopic properties of members
This paper is the first of a series addressed to the investigation of galaxy
formation/evolution in small scale systems of galaxies (SSSGs) which are
located in low density cosmic environments. Our algorithm for SSSG selection
includes galaxy systems of 2 or more galaxies lying within 1000 km/s and a 200
h_{100}^{-1} kpc radius volume. We present the analysis of the photometric and
spectroscopic properties of 19 member galaxies belonging to a sample of 11
SSSGs.
In the plane, early-type members may be considered "ordinary",
not "bright" galaxies in the definition given by Capaccioli et al.(1992) with a
significant fraction of galaxies having a disk or disky isophotes. We do not
detect fine structure and signatures of recent interaction events in the
early-type galaxy population, a picture also confirmed by the spectroscopy.
At odd, there are several spiral members with open arm configurations as
expected in interacting systems. At the same time, emission lines in the
spectra of spiral members fall in the HII regions regime defined with
diagnostic diagrams (Veilleux & Osterbrock 1987). None of the objects displays
unambiguous indication of nuclear activity, although fourspiral nuclei could be
ascribed to the class of Seyferts. The star formation rate seems enhanced over
the average expected in spiral galaxies only for poorer SSSGs in particular
pairs (<50 solar masses per year) but without being in the range of starburst
systems.Comment: 24 pages, including 6 figures and 6 tables. Accepted for publication
in A
Generalized Jacobi identities and ball-box theorem for horizontally regular vector fields
We consider a family of vector fields and we assume a horizontal regularity
on their derivatives. We discuss the notion of commutator showing that
different definitions agree. We apply our results to the proof of a ball-box
theorem and Poincar\'e inequality for nonsmooth H\"ormander vector fields.Comment: arXiv admin note: material from arXiv:1106.2410v1, now three separate
articles arXiv:1106.2410v2, arXiv:1201.5228, arXiv:1201.520
Halloysite nanotubes as promising candidates for the preparation of Polyamide-6 nanocomposites
Halloysite is a polymorph of kaolinite which naturally wraps itself to form tubular structures. Due to its availability, low cost and morphology, it has gained attention in numerous fields of application, including functional coatings and polymer nanocomposites [1]. It is particularly suited to the filler role as it is cheap, thermally and mechanically resistant, and characterized by a high aspect ratio, crucial to guarantee strong polymer-filler interactions [2]. Clay powders are widely adopted as flame retardant additives at high percentages. The application of halloysite nanotubes (HNT) as additives at low contents for the tailoring of the mechanical and thermal properties of polymer composites has been instead much less investigated [3]. Our group investigated the use of HNT as additive at low content (< 5%w) in polyamide-6 (PA6) nanocomposites, due to its wide range of industrial application and relatively poor thermal and mechanical properties. Two different commercial HNT samples were adopted, showing different aspect ratios and purity (Fig. 1). The surface properties of both materials were modulated by functionalization with (3 aminopropyl)triethoxysilane (APTES). Samples were extensively characterized by TEM, BET, FTIR spectroscopy and \u3b6-potential measurements. Both extrusion and in-synthesis addition were tested, and the resulting nanocomposites were characterized by TGA, DSC, GPC, DMA and rheology measurements. Preliminary results suggest that the addition of HNT produces an increase in the crystallization temperature; the presence of HNT in the polymer matrix appears to favour the formation of the \u3b3 phase of PA6. While APTES functionalization eased the filler incorporation during extrusion, it lowered the shear rate of the starting polymer. The obtained results suggested a large room for tunability of the properties of PA6/HNT nanocomposites
Small-scale systems of galaxies. II. Properties of the NGC 4756 group of galaxies
We present results from a study of the NGC 4756 group which is dominated by
the elliptical galaxy NGC 5746. The characteristics of the group are
investigated through (a) the detailed investigation of the morphological,
photometric and spectroscopic properties of nine galaxies among the dominant
members of the group (b) the determination of the photometric parameters of the
faint galaxy population in an area of 34'x34' centered on NGC 4756 and (c) an
analysis of the X-ray emission in the area based upon archival data. The 9
member galaxies are located in the core part of the NGC 4756 group (a strip
diameter about 300 kpc in diameter which has a very loose configuration. The
central part of the NGC 4756 group contains a significant fraction of
early-type galaxies. Three new group members with previously unknown systemic
velocities are identified, one of which is a dE. At about 7.5' SW of NGC 4756 a
sub-structure of the group is detected, including IC 829, MCG -2-33-35, MCG
-2-33-36 and MCG -2-33-38, which meets the Hickson criteria for being a compact
group. Most of the galaxies in this sub-structure show interaction signatures.
We do not detect apparent fine structure and signatures of recent interaction
events in the early-type galaxy population, with the exception of a strong dust
lane in the elliptical MCG -2-33-38. This galaxy displays however signatures of
nuclear activity. Strong [O III], [N II] and [S II] line emission, combined
with comparatively weak, but broad H alpha emission suggest an intermediate
Seyfert type classification. Although the area is heavily contaminated by the
background cluster Abell 1631, X-ray data suggest the presence of a hot
intergalactic medium related to the group to the X-ray emission detected. The
present results are discussed in the context of group evolution.Comment: 45 pages including 10 figures and 8 tables accepted for publication
in A
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