45,903 research outputs found
Nano-building block based-hybrid organic–inorganic copolymers with self-healing properties
New dynamic materials, that can repair themselves after strong damage, have been designed by hybridization of polymers with structurally well-defined nanobuilding units. The controlled design of cross-linked poly(n-butyl acrylate) (pBuA) has been performed by introducing a very low amount of a specific tin oxo-cluster. Sacrificial domains with non-covalent interactions (i.e. ionic bonds) developed at the hybrid interface play a double role. Such interactions are strong enough to cross-link the polymer, which consequently exhibits rubber-like elasticity behavior and labile enough to enable, after severe mechanical damage, dynamic bond recombination leading to an efficient healing process at room temperature. In agreement with the nature of the reversible links at the hybrid interface, the healing process can speed up considerably with temperature. 1H and 119Sn PFG NMR has been used to evidence the dynamic nature of these peculiar cross-linking nodes
Water vapor and silicon monoxide maser observations in the protoplanetary nebula OH 231.8+4
OH 231.8+4.2 is a well studied preplanetary nebula (pPN) around a binary
stellar system that shows a remarkable bipolar outflow. To study the structure
and kinematics of the inner 10-80 AU nebular regions we performed
high-resolution observations of the HO 6--5 and SiO
=2, =1--0 maser emissions with the Very Long Baseline Array. The absolute
position of both emission distributions were recovered using the phase
referencing technique, and accurately registered in HST optical images. HO
maser clumps are found to be distributed in two areas of 20 mas in size
spatially displaced by 60 milli-arcseconds along an axis oriented nearly
north-south. SiO masers are tentatively found to be placed between the two
HO maser emitting regions, probably indicating the position of the Mira
component of the system. The SiO maser emission traces an inner equatorial
component with a diameter of 12 AU, probably a disk rotating around the M-type
star. Outwards, we detect in the HO data a pair of polar caps, separated by
80 AU. We believe that the inner regions of the nebula probably have been
altered by the presence of the companion, leading to an equator-to-pole density
contrast that may explain the lack of HO masers and strong SiO maser
emission in the denser, equatorial regions.Comment: 5 pages, 1 figure, A&A accepte
PPAK Wide-field Integral Field Spectroscopy of NGC 628: I. The largest spectroscopic mosaic on a single galaxy
We present a wide-field IFS survey on the nearby face-on Sbc galaxy NGC 628,
comprising 11094 individual spectra, covering a nearly circular field-of-view
of ~6 arcmin in diameter, with a sampling of ~2.7 arcsec per spectrum in the
optical wavelength range (3700--7000 AA). This galaxy is part of the PPAK IFS
Nearby Galaxies Survey, (PINGS, Rosales-Ortega et al. 2009). To our knowledge,
this is the widest spectroscopic survey ever made in a single nearby galaxy. A
detailed flux calibration was applied, granting a spectrophotometric accuracy
of \,0.2 mag.
The age of the stellar populations shows a negative gradient from the inner
(older) to the outer (younger) regions. We found an inversion of this gradient
in the central ~1 kpc region, where a somewhat younger stellar population is
present within a ring at this radius. This structure is associated with a
circumnuclear star-forming region at ~ 500 pc, also found in similar spiral
galaxies. From the study of the integrated and spatially resolved ionized gas
we found a moderate SFR of ~ 2.4 Msun yr. The oxygen abundance shows a a
clear gradient of higher metallicity values from the inner part to the outer
part of the galaxy, with a mean value of 12~+~log(O/H) ~ 8.7. At some specific
regions of the galaxy, the spatially resolved distribution of the physical
properties show some level of structure, suggesting real point-to-point
variations within an individual \hh region. Our results are consistent with an
inside-out growth scheme, with stronger star formation at the outer regions,
and with evolved stellar populations in the inner ones.Comment: 31 pages, 22 Figuras, Accepted for Publishing in MNRAS (corrected
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