1,033 research outputs found
An algorithm for the Cartan-Dieudonn\'e theorem on generalized scalar product spaces
We present an algorithmic proof of the Cartan-Dieudonn\'e theorem on
generalized real scalar product spaces with arbitrary signature. We use
Clifford algebras to compute the factorization of a given orthogonal
transformation as a product of reflections with respect to hyperplanes. The
relationship with the Cartan-Dieudonn\'e-Scherk theorem is also discussed in
relation to the minimum number of reflections required to decompose a given
orthogonal transformation.Comment: 25 page
Central Stellar Populations of S0 Galaxies in The Fornax Cluster
Based on FORS2-VLT long-slit spectroscopy, the analysis of the central
absorption line indices of 9 S0 galaxies in the Fornax Cluster is presented.
Central indices correlate with central velocity dispersions as observed in
ellipticals. However, the stellar population properties of these S0s indicates
that the observed trends are produced by relative differences in age and
alpha-element abundances and not in metallicity ([Fe/H]) as previous studies
have found in elliptical galaxies. The observed scatter in the line indices vs.
velocity dispersion relations can be partially explained by the
rotationally-supported nature of many of these systems. The presence of tighter
line indices vs. maximum (circular) rotational velocity relations confirms this
statement. It was also confirmed that the dynamical mass is the driving
physical property of all these correlations and in our Fornax S0s it has to be
estimated assuming rotational support.Comment: To appear in the Proceedings of IAU Symposium 241: "Stellar
Populations as Building Blocks of Galaxies", 10-16 December, 2006 at La
Palma, Canary Islands, Spai
Jointly they edit: examining the impact of community identification on political interaction in Wikipedia
In their 2005 study, Adamic and Glance coined the memorable phrase "divided
they blog", referring to a trend of cyberbalkanization in the political
blogosphere, with liberal and conservative blogs tending to link to other blogs
with a similar political slant, and not to one another. As political discussion
and activity increasingly moves online, the power of framing political
discourses is shifting from mass media to social media. Continued examination
of political interactions online is critical, and we extend this line of
research by examining the activities of political users within the Wikipedia
community. First, we examined how users in Wikipedia choose to display (or not
to display) their political affiliation. Next, we more closely examined the
patterns of cross-party interaction and community participation among those
users proclaiming a political affiliation. In contrast to previous analyses of
other social media, we did not find strong trends indicating a preference to
interact with members of the same political party within the Wikipedia
community. Our results indicate that users who proclaim their political
affiliation within the community tend to proclaim their identity as a
"Wikipedian" even more loudly. It seems that the shared identity of "being
Wikipedian" may be strong enough to triumph over other potentially divisive
facets of personal identity, such as political affiliation.Comment: 33 pages, 5 figure
Los concilios provinciales en Nueva España. Reflexiones e influencias. [Reseña]
Reseña de: María del Pilar MARTÍNEZ LÓPEZ CANO -
Francisco Javier CERVANTES BELLO (coords.),
Los concilios provinciales en Nueva España.
Reflexiones e influencias, Instituto de Investigaciones
Históricas, UNAM, México 2005, 430
pp
Composite scaffold obtained by electro-hydrodynamic technique for infection prevention and treatment in bone repair
Bone infection is a devastating condition resulting from implant or orthopaedic surgery. Therapeutic strategies are extremely complicated and may result in serious side effects or disabilities. The development of enhanced 3D scaffolds, able to promote efficient bone regeneration, combined with targeted antibiotic release to prevent bacterial colonization, is a promising tool for the successful repair of bone defects. Herein, polymeric electrospun scaffolds composed of polycaprolactone (PCL) nanofibres decorated with poly(lactic-co-glycolic acid) (PLGA) particles loaded with rifampicin were fabricated to achieve local and sustained drug release for more efficient prevention and treatment of infection. The release profile showed an initial burst of rifampicin in the first six hours, enabling complete elimination of bacteria. Sustained and long-term release was observed until the end of the experiments (28 days), facilitating a prolonged effect on the inhibition of bacterial growth, which is in agreement with the common knowledge concerning the acidic degradation of the microparticles. In addition, bactericidal effects against gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria were demonstrated at concentrations of released rifampicin up to 58 ppm after 24 h, with greater efficacy against S. aureus (13 ppm vs 58 ppm for E. coli). Cell morphology and cytocompatibility studies highlighted the suitability of the fabricated scaffolds to support cell growth, as well as their promising clinical application for bone regeneration combined with prevention or treatment of bacterial infection
Rotational Correlation Functions of Single Molecules
Single molecule rotational correlation functions are analyzed for several
reorientation geometries. Even for the simplest model of isotropic rotational
diffusion our findings predict non-exponential correlation functions to be
observed by polarization sensitive single molecule fluorescence microscopy.
This may have a deep impact on interpreting the results of molecular
reorientation measurements in heterogeneous environments.Comment: 5 pages, 4 figure
Production, characterization and testing of antibacterial PVA membranes loaded with HA-Ag3PO4 nanoparticles, produced by SC-CO2 phase inversion
BACKGROUND: Silver-loaded hydroxyapatite nanoparticles were incorporated into poly(vinyl alcohol) (PVA) membranes obtained by supercritical CO2 (SC-CO2) assisted phase inversion. Ag3PO4 crystals of 2.2 ± 0.6 nm were dispersed in synthesized needle-like hydroxyapatite nanoparticles (20 × 65 nm) and were uniformly deposited on the internal surfaces of the PVA membranes. Operative conditions to produce membranes by SC-CO2, PVA concentration and the effect on membrane porosity and morphology were studied. RESULTS: Solutions at 20% w/w PVA produced membranes with cellular morphology and nanoporous walls, whereas 30% and 50% w/w solutions produced nanostructured membranes. Silver ions were released from PVA membranes mainly by diffusion according to the Peppas–Sahlin model. Membranes obtained at 20% w/w PVA showed a significant E. coli inhibition at an Ag concentration of 9 ppm, reaching the minimal inhibitory concentration (MIC) and improving the bactericidal activity of the nanoparticles. CONCLUSION: A concentration of Ag3PO4 crystals of about 22 ppm was calculated as being capable of completely destroying these bacteria, reaching the minimum bactericidal concentration (MBC)
Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1
We have obtained new deep optical and near-infrared images of the field of
the radio-loud quasar 1335.8+2834 at where an excess in the surface
number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324]
from optical data. We found a significant clustering of objects with very red
optical-near infrared colors, and near the quasar. The colors and magnitudes of the reddest objects
are consistent with those of old (12 Gyr old at z=0) passively-evolving
elliptical galaxies seen at , clearly defining a `red envelope' like
that found in galaxy clusters at similar or lower redshifts. This evidence
strongly suggests that the quasar resides in a moderately-rich cluster of
galaxies (richness-class ). There is also a relatively large fraction
of objects with moderately red colors () which have a
distribution on the sky similar to that of the reddest objects. They may be
interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS
file. Accepted for ApJ, Letter
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