387 research outputs found
From Giant H II regions and H II galaxies to globular clusters and compact dwarf ellipticals
Massive starforming regions like Giant HII Regions (GHIIR) and HII Galaxies
(HIIG) are emission line systems ionized by compact young massive star clusters
(YMC) with masses ranging from M to M. We model the
photometric and dynamical evolution over a Hubble time of the massive
gravitationally bound systems that populate the tight relation between absolute
blue magnitude and velocity dispersion () of GHIIR and HIIG and
compare the resulting relation with that one of old stellar systems: globular
clusters, elliptical galaxies, bulges of spirals. After 12~Gyr of evolution
their position on the vs. M plane coincides -- depending on the
initial mass -- either with the globular clusters for systems with initial mass
M or with a continuation of the ellipticals, bulges of
spirals and ultracompact dwarfs for YMC with M. The slope
change in the and -size relations at cluster masses around
M is due to the larger impact of the dynamical evolution on the
lower mass clusters. We interpret our result as an indication that the YMC that
ionize GHIIR and HIIG can evolve to form globular clusters and ultra compact
dwarf ellipticals in about 12 Gyr so that present day globular clusters and
ultra compact dwarf ellipticals may have formed in conditions similar to those
observed in today GHIIR and HIIG.Comment: 11 pages, 6 figures, accepted for publication in MNRA
Influence of substitution model selection on protein phylogenetic tree reconstruction
Probabilistic phylogenetic tree reconstruction is traditionally performed under a best-fitting substitution model of molecular evolution previously selected according to diverse statistical criteria. Interestingly, some recent studies proposed that this procedure is unnecessary for phylogenetic tree reconstruction leading to a debate in the field. In contrast to DNA sequences, phylogenetic tree reconstruction from protein sequences is traditionally based on empirical exchangeability matrices that can differ among taxonomic groups and protein families. Considering this aspect, here we investigated the influence of selecting a substitution model of protein evolution on phylogenetic tree reconstruction by the analyses of real and simulated data. We found that phylogenetic tree reconstructions based on a selected best-fitting substitution model of protein evolution are the most accurate, in terms of topology and branch lengths, compared with those derived from substitution models with amino acid replacement matrices far from the selected best-fitting model, especially when the data has large genetic diversity. Indeed, we found that substitution models with similar amino acid replacement matrices produce similar reconstructed phylogenetic trees, suggesting the use of substitution models as similar as possible to a selected best-fitting model when the latter cannot be used. Therefore, we recommend the use of the traditional protocol of selection among substitution models of evolution for protein phylogenetic tree reconstruction.Universidade de Vigo/CISUGAgencia Estatal de Investigación | Ref. PID2019-107931GA-I0
An independent determination of the local Hubble constant
The relationship between the integrated H line luminosity and the
velocity dispersion of the ionized gas of HII galaxies and giant HII regions
represents an exciting standard candle that presently can be used up to
redshifts z ~ 4. Locally it is used to obtain precise measurements of the
Hubble constant by combining the slope of the relation obtained from nearby ( 0.2) HII galaxies with the zero point determined from giant HII regions
belonging to an `anchor sample' of galaxies for which accurate
redshift-independent distance moduli are available. We present new data for 36
giant HII regions in 13 galaxies of the anchor sample that includes the
megamaser galaxy NGC 4258. Our data is the result of the first four years of
observation of our primary sample of 130 giant HII regions in 73 galaxies with
Cepheid determined distances. Our best estimate of the Hubble parameter is
km /s Mpc This result is the product of
an independent approach and, although at present less precise than the latest
SNIa results, it is amenable to substantial improvement.Comment: 30 pages, 28 figures, Accepted to be published in MNRA
Analysis of selection in protein-coding sequences accounting for common biases
The evolution of protein-coding genes is usually driven by selective processes, which favor some evolutionary trajectories over others, optimizing the subsequent protein stability and activity. The analysis of selection in this type of genetic data is broadly performed with the metric nonsynonymous/synonymous substitution rate ratio (dN/dS). However, most of the well-established methodologies to estimate this metric make crucial assumptions, such as lack of recombination or invariable codon frequencies along genes, which can bias the estimation. Here, we review the most relevant biases in the dN/dS estimation and provide a detailed guide to estimate this metric using state-of-the-art procedures that account for such biases, along with illustrative practical examples and recommendations. We also discuss the traditional interpretation of the estimated dN/dS emphasizing the importance of considering complementary biological information such as the role of the observed substitutions on the stability and function of proteins. This review is oriented to help evolutionary biologists that aim to accurately estimate selection in protein-coding sequences.Agencia Estatal de Investigación | Ref. RYC-2015-18241Agencia Estatal de Investigación | Ref. IJCI-2016-29550Xunta de Galicia | Ref. ED431F 2018/08Fundação para a Ciência e a Tecnologia | Ref. SFRH/BD/143607/201
The L - \sigma\ relation for HII galaxies in green
The correlation between emission-line luminosity (L) and profile width
(sigma) for HII Galaxies provides a powerful method to measure the distances to
galaxies over a wide range of redshifts. In this paper we use SDSS
spectrophotometry to explore the systematics of the correlation using the
[OIII]5007 lines instead of Halpha or Hbeta to measure luminosities and line
widths. We also examine possible systematic effects involved in measuring the
profile-widths and the luminosities through different apertures. We find that
the green L-sigma relation defined using [OIII]5007 luminosities is
significantly more sensitive than Hbeta to the effects of age and the physical
conditions of the nebulae, which more than offsets the advantage of the higher
strength of the [OIII]5007 lines. We then explore the possibility of mixing
[OIII]5007 profile-widths with SDSS Hbeta luminosities using the Hubble
constant H0 to quantify the possible systematic effects. We find the mixed
L(Hbeta) sigma[OIII] relation to be at least as powerful as the canonical
L-sigma relation as a distance estimator, and we show that the evolutionary
corrections do not change the slope and the scatter of the correlation, and
therefore, do not bias the L-sigma distance indicator at high redshifts.
Locally, however, the luminosities of the Giant HII Regions that provide the
zero-point calibrators are sensitive to evolutionary corrections and may bias
the Hubble constant if their mean ages, as measured by the equivalent widths of
Hbeta, are significantly different from the mean age of the HII Galaxies. Using
a small sample of 16 ad-hoc zero point calibrators we obtain a value of H0 =
66.4\pm4.5 km s^-1 Mpc^-1 for the Hubble constant, which is fully consistent
with the best modern determinations, and that is not biased by evolutionary
corrections.Comment: 14 pages, 7 figures. Accepted for publication by A&
The influence of heterogeneous codon frequencies along sequences on the estimation of molecular adaptation
Motivation: The nonsynonymous/synonymous substitution rate ratio (dN/dS) is a commonly used parameter to quantify molecular adaptation in protein-coding data. It is known that the estimation of dN/dS can be biased if some evolutionary processes are ignored. In this concern, common ML methods to estimate dN/dS assume invariable codon frequencies among sites, despite this characteristic is rare in nature, and it could bias the estimation of this parameter. Results: Here we studied the influence of variable codon frequencies among genetic regions on the estimation of dN/dS. We explored scenarios varying the number of genetic regions that differ in codon frequencies, the amount of variability of codon frequencies among regions and the nucleotide frequencies at each codon position among regions. We found that ignoring heterogeneous codon frequencies among regions overall leads to underestimation of dN/dS and the bias increases with the level of heterogeneity of codon frequencies. Interestingly, we also found that varying nucleotide frequencies among regions at the first or second codon position leads to underestimation of dN/dS while variation at the third codon position leads to overestimation of dN/dS. Next, we present a methodology to reduce this bias based on the analysis of partitions presenting similar codon frequencies and we applied it to analyze four real datasets. We conclude that accounting for heterogeneous codon frequencies along sequences is required to obtain realistic estimates of molecular adaptation through this relevant evolutionary parameter. Availability and implementation: The applied frameworks for the computer simulations of protein-coding data and estimation of molecular adaptation are SGWE and PAML, respectively. Both are publicly available and referenced in the study. Supplementary information: Supplementary data are available at Bioinformatics online.Ministerio de EconomÃa y Competitividad | Ref. RYC-2015-18241Agencia Estatal de Investigación | Ref. IJCI-2016-29550Xunta de Galicia | Ref. ED431F 2018/0
Sound-Absorption Properties of Materials Made of Esparto Grass Fibers
[EN] Research on sound-absorbing materials made of natural fibers is an emerging area in sustainable materials. In this communication, the use of raw esparto grass as an environmentally friendly sound-absorbing material is explored. Measurements of the normal-incidence sound-absorption coefficient and airflow resistivity of three different types of esparto from different countries are presented. In addition, the best-fit coefficients for reasonable prediction of the sound-absorption performance by means of simple empirical formulae are reported. These formulae require only knowledge of the airflow resistivity of the fibrous material. The results presented in this paper are an addition to the characterization of available natural fibers to be used as alternatives to synthetic ones in the manufacturing of sound-absorbing materials.This research was funded by CONICYT-FONDECYT, grant number 1171110.Arenas, JP.; Rey Tormos, RMD.; Alba, J.; Oltra, R. (2020). 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