Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical composition analysis and metallicity-luminosity relations

(Abridged) We performed a multiwavelength analysis of a sample of starburst galaxies that show the presence of a substantial population of very young massive (WR) stars. Here we present the global analysis of the derived photometric and chemical properties. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties with previous observations and galaxy evolution models. Attending to their absolute B-magnitude many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both C(Hb) and Wabs increase with increasing metallicity. We detected a high N/O ratio in objects showing strong WR features. The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained using empirical calibrations, finding that (i) the Pilyugin method is the best suitable empirical calibration, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are related to the optical/NIR luminosity; the dispersion is consequence of the differences in the star-formation histories. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Our detailed analysis is fundamental to understand the nature of galaxies showing strong starbursts, as well as to know their star formation history and the relationships with the environment.Comment: 30 pages, 22 figures, accepted to A&A. Updated with the final version

The tidally disturbed luminous compact blue galaxy Mkn 1087 and its surroundings

We present new broad-band optical and near-infrared CCD imaging together with deep optical intermediate-resolution spectroscopy of Mkn 1087 and its surrounding objects. We analyze the morphology and colors of the stellar populations of the brightest objects, some of them star-formation areas, as well as the kinematics, physical conditions and chemical composition of the ionized gas associated with them. Mkn 1087 does not host an Active Galactic Nucleus, but it could be a Luminous Compact Blue Galaxy. Although it was classified as a suspected Wolf-Rayet galaxy, we do not detect the spectral features of these sort of massive stars. Mkn 1087 shows morphological and kinematical features that can be explained assuming that it is in interaction with two nearby galaxies: the bright KPG 103a and a dwarf ($M_B\sim-18$) star-forming companion. We argue that this dwarf companion is not a tidal object but an external galaxy because of its low metallicity [12+log(O/H) = 8.24] with respect to the one derived for Mkn 1087 [12+log(O/H) = 8.57] and its kinematics. Some of the non-stellar objects surrounding Mkn 1087 are connected by bridges of matter with the main body, host star-formation events and show similar abundances despite their different angular distances. These facts, together their kinematics, suggest that they are tidal dwarf galaxies formed from material stripped from Mkn 1087. A bright star-forming region at the south of Mkn 1087 (knot #7) does not show indications of being a tidal galaxy or the product of a merging process as suggested in previous works. We argue that Mkn 1087 and its surroundings should be considered a group of galaxies.Comment: Accepted by A&A, 21 pages, 13 figures, 8 table

Evaluation of the Effects of Predicted Associativity on the Reliability and Performance of Mobile Ad Hoc Networks

Routing in Mobile Ad Hoc Networks (MANETs) presents unique challenges not encountered in conventional networks. Predicted Associativity Routing (PAR) is a protocol designed to address reliability in MANETs. Using associativity information, PAR calculates the expected lifetime of neighboring links. Nodes use this expected lifetime, and their neighbor\u27s connectivity to determine a residual lifetime. The routes are selected from those with the longest residual lifetimes. In this way, PAR attempts to improve the reliability of discovered routes. PAR is compared to AODV using a variety of reliability and performance metrics. Despite its focus on reliability, PAR does not provide more reliable routes. Rather, AODV produces routes which last as much as three times longer than PAR. However, PAR delivers more data and has greater throughput. Both protocols are affected most by the node density of the networks. Node density accounts for 48.62% of the variation in route lifetime in AODV, and 70.66% of the variation in PAR. As node density increases from 25 to 75 nodes route lifetimes are halved, while throughput increases drastically with the increased routing overhead. Furthermore, PAR increases end-to-end delay, while AODV displays better efficiency

Genome wide comparative analysis of the effects of PRMT5 and PRMT4/CARM1 arginine methyltransferases on the Arabidopsis thaliana transcriptome

BACKGROUND: Methylation at arginine residues (R) is an important post-translational modification that regulates a myriad of essential cellular processes in eukaryotes, such as transcriptional regulation, RNA processing, signal transduction and DNA repair. Arginine methylation is catalyzed by a family of enzymes known as protein arginine methyltransferases (PRMTs). PRMTs are classified as Type I or Type II, depending on the position of the methyl group on the guanidine of the methylated arginine. Previous reports have linked symmetric R methylation to transcriptional repression, while asymmetric R methylation is generally associated with transcriptional activation. However, global studies supporting this conclusion are not available. RESULTS: Here we compared side by side the physiological and molecular roles of the best characterized plant PRMTs, the Type II PRMT5 and the Type I PRMT4, also known as CARM1 in mammals. We found that prmt5 and prmt4a;4b mutants showed similar alterations in flowering time, photomorphogenic responses and salt stress tolerance, while only prmt5 mutants exhibited alterations in circadian rhythms. An RNA-seq analysis revealed that expression and splicing of many differentially regulated genes was similarly enhanced or repressed by PRMT5 and PRMT4s. Furthermore, PRMT5 and PRMT4s co-regulated the expression and splicing of key regulatory genes associated with transcription, RNA processing, responses to light, flowering, and abiotic stress tolerance, being candidates to mediate the physiological alterations observed in the mutants. CONCLUSIONS: Our global analysis indicates that two of the most important Type I and Type II arginine methyltransferases, PRTM4 and PRMT5, have mostly overlapping as well as specific, but not opposite, roles in the global regulation of gene expression in plants.Fil: Hernando, Carlos Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Sanchez, Sabrina Elena. University of Southern California; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Mancini, Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Yanovsky, Marcelo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

Stochastic vortex dynamics in two-dimensional easy-plane ferromagnets: Multiplicative versus additive noise

We study how thermal fluctuations affect the dynamics of vortices in the two-dimensional classical, ferromagnetic, anisotropic Heisenberg model depending on their additive or multiplicative character. Using a collective coordinate theory, we analytically show that multiplicative noise, arising from fluctuations in the local field term of the Landau-Lifshitz equations, and Langevin-like additive noise both have the same effect on vortex dynamics (within a very plausible assumption consistent with the collective coordinate approach). This is a non-trivial result, as multiplicative and additive noises usually modify the dynamics quite differently. We also carry out numerical simulations of both versions of the model finding that they indeed give rise to very similar vortex dynamics.Comment: 10 pages, 6 figure

Adenocarcinoma gástrico

Young and white people are more likely to have proximal gastric cancer, while the Asian, African American, and Hispanic population are more likely to have distal cancers. Helicobacter pylori is the predominant risk factor for Gastric Cancer. The symptoms of gastric cancer are not specific and can mimic other non-neoplastic gastroduodenal diseases. Surgical resection is the only treatment for gastric Ca, but in an advanced stage of Ca prevents curative resection for most patientsLas personas jóvenes y blancas son más propensas a tener cáncer gástrico proximal, mientras que la población asiática, afroamericana e hispana tienen más probabilidades de tener cáncer distal. Helicobacter pylori es el factor de riesgo predominante para el cáncer gástrico. Los síntomas del cáncer gástrico no son específicos y pueden simular otras enfermedades gastroduodenales no neoplásicas. La resección quirúrgica es el único tratamiento para el Ca gástrico, pero en una etapa avanzada de Ca previene la resección curativa para la mayoría de los paciente