276 research outputs found
"Magic" numbers in Smale's 7th problem
Smale's 7-th problem concerns N-point configurations on the 2-dim sphere
which minimize the logarithmic pair-energy V_0(r) = -ln r averaged over the
pairs in a configuration; here, r is the chordal distance between the points
forming a pair. More generally, V_0(r) may be replaced by the standardized
Riesz pair-energy V_s(r)= (r^{-s} -1)/s, which becomes - ln r in the limit s to
0, and the sphere may be replaced by other compact manifolds. This paper
inquires into the concavity of the map from the integers N>1 into the minimal
average standardized Riesz pair-energies v_s(N) of the N-point configurations
on the 2-sphere for various real s. It is known that v_s(N) is strictly
increasing for each real s, and for s<2 also bounded above, hence "overall
concave." It is (easily) proved that v_{-2}(N) is even locally strictly
concave, and that so is v_s(2n) for s<-2. By analyzing computer-experimental
data of putatively minimal average Riesz pair-energies v_s^x(N) for s in
{-1,0,1,2,3} and N in {2,...,200}, it is found that {v}_{-1}^x(N) is locally
strictly concave, while v_s^x(N) is not always locally strictly concave for s
in {0,1,2,3}: concavity defects occur whenever N in C^{x}_+(s) (an s-specific
empirical set of integers). It is found that the empirical map C^{x}_+(s), with
s in {-2,-1,0,1,2,3}, is set-theoretically increasing; moreover, the percentage
of odd numbers in C^{x}_+(s), s in {0,1,2,3}, is found to increase with s. The
integers in C^{x}_+(0) are few and far between, forming a curious sequence of
numbers, reminiscent of the "magic numbers" in nuclear physics. It is
conjectured that the "magic numbers" in Smale's 7-th problem are associated
with optimally symmetric optimal-energy configurations.Comment: 109 pages, of which 30 are numerical data tables. Thoroughly revised
version, to appear in J. Stat. Phys. under the different title: `Optimal N
point configurations on the sphere: "Magic" numbers and Smale's 7th problem
Globular Clusters: DNA of Early-Type galaxies?
This paper explores if the mean properties of Early-Type Galaxies (ETG) can
be reconstructed from "genetic" information stored in their GCs (i.e., in their
chemical abundances, spatial distributions and ages). This approach implies
that the formation of each globular occurs in very massive stellar
environments, as suggested by some models that aim at explaining the presence
of multi-populations in these systems. The assumption that the relative number
of globular clusters to diffuse stellar mass depends exponentially on chemical
abundance, [Z/H], and the presence of two dominant GC sub-populations blue and
red, allows the mapping of low metallicity halos and of higher metallicity (and
more heterogeneous) bulges. In particular, the masses of the low-metallicity
halos seem to scale up with dark matter mass through a constant. We also find a
dependence of the globular cluster formation efficiency with the mean projected
stellar mass density of the galaxies within their effective radii. The analysis
is based on a selected sub-sample of galaxies observed within the ACS Virgo
Cluster Survey of the {\it Hubble Space Telescope}. These systems were grouped,
according to their absolute magnitudes, in order to define composite fiducial
galaxies and look for a quantitative connection with their (also composite)
globular clusters systems. The results strengthen the idea that globular
clusters are good quantitative tracers of both baryonic and dark matter in
ETGs.Comment: 20 pages, 28 figures and 5 table
New poly(ionic liquid)s based on poly(azomethine-pyridinium) salts and its use as heterogeneous catalysts for CO2 conversion
A fast and simple synthetic route towards a new family of poly(ionic liquids) based on aromatic crosslinked poly(azomethine-pyridinium) salts is described. These new polymers were prepared in one step from new diamine methyl pyridinium salts and isopthaldehyde, in 30âŻmin under microwave irradiation. By this method, poly(azomethine-pyridinium) containing chloride (Cl), bis(trifluoromethylsulfonyl)imide (TFSI) and hexaflorophosphate (PF6) as counter-anions were synthetized. This new pyridinium poly(ionic liquid)s were obtained as insoluble powders showing high thermal stability. The poly(azomethine-pyridinium)s were tested as heterogeneous catalysts in the cycloaddition of CO2 to epichlorohydrin to obtain chloropropylene carbonate. The polymers containing chloride anion shows high content of catalytically active sites and the best performance of the series, with 100% selectivity towards the chloropropylene carbonate in a reaction without solvent at 3âŻbar of CO2, 100âŻÂ°C and low catalyst loading (0.5âŻmol%).Spanish Government, MINECO (Projects MAT2014-52085-C2-2-P and MAT2017-82288-C2-2-P, MAT2017-83373-R
P02.23. The efficacy of prolotherapy using dextrose-morrhuate for lateral epicondylosis: a pilot randomized controlled trial
The Brazil-Argentina gemini group for the study of globular cluster systems (BAGGs GCs): Flamingos-2 and GMOS data for NGC 1395
In this letter, we present preliminary results of the analysis of Flamingos-2 and GMOS-S photometry of the globular cluster (GC) system of the elliptical galaxy NGC1395. This is the first step of a long-term Brazilian-Argentinian collaboration for the study of GC systems in early-type galaxies. In the context of this collaboration, we obtained deep NIR photometric data in two different bands (J and Ks), which were later combined with high quality optical Gemini + GMOS photometry previously obtained by the Argentinian team. This allowed us to obtain different color indices, less sensitive to the effect of horizontal branch (HB) stars for several hundreds of GC candidates, and to make an initial assessment of the presence or absence of multiple GC populations in colors in NGC1395.Instituto de AstrofĂsica de La PlataMuseo de AstronomĂa y GeofĂsic
The Brazil-Argentina gemini group for the study of globular cluster systems (BAGGs GCs): Flamingos-2 and GMOS data for NGC 1395
In this letter, we present preliminary results of the analysis of Flamingos-2 and GMOS-S photometry of the globular cluster (GC) system of the elliptical galaxy NGC1395. This is the first step of a long-term Brazilian-Argentinian collaboration for the study of GC systems in early-type galaxies. In the context of this collaboration, we obtained deep NIR photometric data in two different bands (J and Ks), which were later combined with high quality optical Gemini + GMOS photometry previously obtained by the Argentinian team. This allowed us to obtain different color indices, less sensitive to the effect of horizontal branch (HB) stars for several hundreds of GC candidates, and to make an initial assessment of the presence or absence of multiple GC populations in colors in NGC1395.Instituto de AstrofĂsica de La PlataMuseo de AstronomĂa y GeofĂsic
Attributing scientific and technical progress: the case of holography
Holography, the three-dimensional imaging technology, was portrayed widely as a paradigm
of progress during its decade of explosive expansion 1964â73, and during its subsequent
consolidation for commercial and artistic uses up to the mid 1980s. An unusually
seductive and prolific subject, holography successively spawned scientific insights, putative
applications and new constituencies of practitioners and consumers. Waves of forecasts,
associated with different sponsors and user communities, cast holography as a field on the
verge of successâbut with the dimensions of success repeatedly refashioned. This retargeting
of the subject represented a degree of cynical marketeering, but was underpinned by
implicit confidence in philosophical positivism and faith in technological progressivism.
Each of its communities defined success in terms of expansion, and anticipated continual
progressive increase. This paper discusses the contrasting definitions of progress in holography,
and how they were fashioned in changing contexts. Focusing equally on reputed âfailuresâ of some aspects of the subject, it explores the varied attributes by which success and failure were linked with progress by different technical communities. This important case illuminates the peculiar post-World War II environment that melded the military, commercial and popular engagement with scientific and technological subjects, and the
competing criteria by which they assessed the products of science
La primera enana ultra-compacta confirmada en el grupo de NGC5044
En el siguiente trabajo confirmamos como miembro del grupo NGC5044, un objeto que por sus propiedades fotomĂ©tricas constituye la primer Enana ultra-compacta âUCDâ (por sus siglas en inglĂ©s) detectada en dicho grupo. La misma se encuentra asociada a la galaxia masiva NGC5044 y fue identificada empleando datos Gemini+GMOS. Se presentan los resultados preliminares de un anĂĄlisis de poblaciones estelares, basado en espectros obtenidos mediante el mismo instrumento. Dicho anĂĄlisis indica que se trata de un objeto masivo (MV ⌠-12.3 mag), con una edad mayor a 10Ă109 años, con metalicidades y abundancias [Z/H] ⌠-1 y [α/Fe] ⌠0.3, respectivamente.In the present work we confirm as a member of the group NGC5044, an object which due to its photometric properties constitutes the first UCD detected in this group. It is associated with the massive galaxy NGC5044 and was identified using Gemini+GMOS data. We present the preliminary results of an analysis of stellar populations, based on spectra obtained by the same instrument. This analysis indicates that this is a massive object (MV ⌠-12.3 mag), older than 10Ă109 years, with metallicity and abundances [Z/H] ⌠-1 and [α/Fe]⌠0.3, respectively.Trabajo publicado en Actas de las Terceras Jornadas de AstrofĂsica Estelar. La Plata, AsociaciĂłn Argentina de AstronomĂa, 2018.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Triggered metal ion release and oxidation: ferrocene as a mechanophore in polymers
The introduction of mechanophores into polymers makes it possible to transduce mechanical forces into chemical reactions that can be used to impart functions such as selfâhealing, catalytic activity, and mechanochromic response. Here, an example of mechanically induced metal ion release from a polymer is reported. Ferrocene (Fc) was incorporated as an iron ion releasing mechanophore into poly(methyl acrylate)s (PMAs) and polyurethanes (PUs). Sonication triggered the preferential cleavage of the polymers at the Fc units over other bonds, as shown by a kinetic study of the molar mass distribution of the cleaved Fcâcontaining and Fcâfree reference polymers. The released and oxidized iron ions can be detected with KSCN to generate the redâ colored [Fe(SCN)n(H2O)6ân)](3ân)+ complex or reacted with K4[Fe(CN)6] to afford Prussian blue
La primera enana ultra-compacta confirmada en el grupo de NGC5044
En el siguiente trabajo confirmamos como miembro del grupo NGC5044, un objeto que por sus propiedades fotomĂ©tricas constituye la primer Enana ultra-compacta âUCDâ (por sus siglas en inglĂ©s) detectada en dicho grupo. La misma se encuentra asociada a la galaxia masiva NGC5044 y fue identificada empleando datos Gemini+GMOS. Se presentan los resultados preliminares de un anĂĄlisis de poblaciones estelares, basado en espectros obtenidos mediante el mismo instrumento. Dicho anĂĄlisis indica que se trata de un objeto masivo (MV ⌠-12.3 mag), con una edad mayor a 10Ă109 años, con metalicidades y abundancias [Z/H] ⌠-1 y [α/Fe] ⌠0.3, respectivamente.In the present work we confirm as a member of the group NGC5044, an object which due to its photometric properties constitutes the first UCD detected in this group. It is associated with the massive galaxy NGC5044 and was identified using Gemini+GMOS data. We present the preliminary results of an analysis of stellar populations, based on spectra obtained by the same instrument. This analysis indicates that this is a massive object (MV ⌠-12.3 mag), older than 10Ă109 years, with metallicity and abundances [Z/H] ⌠-1 and [α/Fe]⌠0.3, respectively.Trabajo publicado en Actas de las Terceras Jornadas de AstrofĂsica Estelar. La Plata, AsociaciĂłn Argentina de AstronomĂa, 2018.Facultad de Ciencias AstronĂłmicas y GeofĂsica
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