Galaxies with Shells in the Illustris Simulation: Metallicity Signatures

Stellar shells are low surface brightness arcs of overdense stellar regions, extending to large galactocentric distances. In a companion study, we identified 39 shell galaxies in a sample of 220 massive ellipticals ($\mathrm{M}_{\mathrm{200crit}}>6\times10^{12}\,\mathrm{M}_\odot$) from the Illustris cosmological simulation. We used stellar history catalogs to trace the history of each individual star particle inside the shell substructures, and we found that shells in high-mass galaxies form through mergers with massive satellites (stellar mass ratios $\mu_{\mathrm{stars}}\gtrsim1:10$). Using the same sample of shell galaxies, the current study extends the stellar history catalogs in order to investigate the metallicity of stellar shells around massive galaxies. Our results indicate that outer shells are often times more metal-rich than the surrounding stellar material in a galaxy's halo. For a galaxy with two different satellites forming $z=0$ shells, we find a significant difference in the metallicity of the shells produced by each progenitor. We also find that shell galaxies have higher mass-weighted logarithmic metallicities ([Z/H]) at $2$-$4\,\mathrm{R}_{\mathrm{eff}}$ compared to galaxies without shells. Our results indicate that observations comparing the metallicities of stars in tidal features, such as shells, to the average metallicities in the stellar halo can provide information about the assembly histories of galaxies.Comment: 15 pages, 5 figures. Article published in a special issue of MDPI Galaxies after the conference "On the Origin (and Evolution) of Baryonic Galaxy Halos", Galapagos Islands, 201

Formation and Incidence of Shell Galaxies in the Illustris Simulation

Shells are low surface brightness tidal debris that appear as interleaved caustics with large opening angles, often situated on both sides of the galaxy center. In this paper, we study the incidence and formation processes of shell galaxies in the cosmological gravity+hydrodynamics Illustris simulation. We identify shells at redshift z=0 using stellar surface density maps, and we use stellar history catalogs to trace the birth, trajectory and progenitors of each individual star particle contributing to the tidal feature. Out of a sample of the 220 most massive galaxies in Illustris ($\mathrm{M}_{\mathrm{200crit}}>6\times10^{12}\,\mathrm{M}_{\odot}$), $18\%\pm3\%$ of the galaxies exhibit shells. This fraction increases with increasing mass cut: higher mass galaxies are more likely to have stellar shells. Furthermore, the fraction of massive galaxies that exhibit shells decreases with increasing redshift. We find that shell galaxies observed at redshift $z=0$ form preferentially through relatively major mergers ($\gtrsim$1:10 in stellar mass ratio). Progenitors are accreted on low angular momentum orbits, in a preferred time-window between $\sim$4 and 8 Gyrs ago. Our study indicates that, due to dynamical friction, more massive satellites are allowed to probe a wider range of impact parameters at accretion time, while small companions need almost purely radial infall trajectories in order to produce shells. We also find a number of special cases, as a consequence of the additional complexity introduced by the cosmological setting. These include galaxies with multiple shell-forming progenitors, satellite-of-satellites also forming shells, or satellites that fail to produce shells due to multiple major mergers happening in quick succession.Comment: 27 pages, 18 figures. Accepted for publication in MNRAS (new figures 3 and D1 + additional minor changes to match accepted version

Formation and Incidence of Shell Galaxies in the Illustris Simulation

Shells are low surface brightness tidal debris that appear as interleaved caustics with large opening angles, often situated on both sides of the galaxy center. In this paper, we study the incidence and formation processes of shell galaxies in the cosmological gravity+hydrodynamics Illustris simulation. We identify shells at redshift z=0 using stellar surface density maps, and we use stellar history catalogs to trace the birth, trajectory and progenitors of each individual star particle contributing to the tidal feature. Out of a sample of the 220 most massive galaxies in Illustris ($\mathrm{M}_{\mathrm{200crit}}>6\times10^{12}\,\mathrm{M}_{\odot}$), $18\%\pm3\%$ of the galaxies exhibit shells. This fraction increases with increasing mass cut: higher mass galaxies are more likely to have stellar shells. Furthermore, the fraction of massive galaxies that exhibit shells decreases with increasing redshift. We find that shell galaxies observed at redshift $z=0$ form preferentially through relatively major mergers ($\gtrsim$1:10 in stellar mass ratio). Progenitors are accreted on low angular momentum orbits, in a preferred time-window between $\sim$4 and 8 Gyrs ago. Our study indicates that, due to dynamical friction, more massive satellites are allowed to probe a wider range of impact parameters at accretion time, while small companions need almost purely radial infall trajectories in order to produce shells. We also find a number of special cases, as a consequence of the additional complexity introduced by the cosmological setting. These include galaxies with multiple shell-forming progenitors, satellite-of-satellites also forming shells, or satellites that fail to produce shells due to multiple major mergers happening in quick succession.Comment: 27 pages, 18 figures. Accepted for publication in MNRAS (new figures 3 and D1 + additional minor changes to match accepted version

Reestructuración de los procesos en el aréa de empaque de LFLOWERS.

La falta de control y supervisión en cualquier nivel organizacional, puede tener un efecto negativo en la rentabilidad de toda organización. Si todas las personas fueren perfectas, todo marcharía a la perfección, sin necesidad de control, pero todos cometemos errores, existen personas olvidadizas, descuidadas, distraídas, con poca calma, etc., y todos como seres humanos que somos, estamos expuestos a cometer errores. Ya que los seres humanos nunca alcanzaran la perfección, es allí donde radica la importancia de la aplicación de controles y mecanismos de supervisión, para detectar lo que se está haciendo mal y tomar los correctivos de inmediato. Esto es la motivación de la realización de este proyecto, ya que son casos muy comunes en las organizaciones y que en caso de las pymes no son tomadas con la importancia que se lo debería hacer. Este proyecto considera que toda organización debe tener bases sólidas, sostenidas desde un adecuado manual de políticas generales que establezca las normas de cumplimiento y a su vez, adecuados mecanismos de supervisión y control que garanticen el cumplimiento de las mismas. De igual manera la aplicación de auditorías para detectar irregularidades y deficiencias, y finalmente aplicar conceptos de reingeniería de procesos, que permita ágilmente modificar procesos deficientes ya sea con el fin de crear nuevos procesos o mejorar los existentes. Son todos estos, conceptos que consideramos esenciales, para toda organización, que tenga como conseguir el logro de objetivos mediante una rentabilidad sostenida, aportando al desarrollo productivo del país

Silica-Coated Magnetic Nanocomposites for Pb2+ Removal from Aqueous Solution

Magnetic iron oxide-silica shell nanocomposites with different iron oxide/silica ratio were synthesized and structurally characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), small-angle neutron scattering, magnetic and N2-sorption studies. The composite that resulted with the best properties in terms of contact surface area and saturation of magnetization was selected for Pb2+ adsorption studies from aqueous media. The material presented good absorption capacit (maximum adsorption capacity 14.9 mg·g−1) comparable with similar materials presented in literature. Its chemico-physical stability and adsorption capacity recommend the nanocomposite as a cheap adsorbent material for lead

Cuspal Deflection and Adhesive Interface Integrity of Low Shrinking Posterior Composite Restorations

Kad je riječ o restaurativnim zahvatima u distalnom području trenuačno su u svim istraživanjima u središtu pozornosti nisko-kontrahirajući kompoziti. U vezi s tim obećavaju materijali dobiveni siloranskim kemijskim postupkom s prstenastim monomerima i kondenzabilni dimetakrilati s visokim postotkom punila. Materijali i metode: Na ekstrahiranim gornjim premolarima (n=10) promatran je otklon kvržica nakon svjetlosne polimerizacije transduserom s razlikovanjem direktne struje (DCDT-om) uz čuvanje adhezivne veze elektronskim mikroskopom (SEM-om) i dvama restorativnim sustavima. To su Filtek™ Silorane/Silorane System Adhesive (3M ESPE) i Premise™ Packable /OptiBond FL (KERR). Podaci su analizirani dvostranim t-testom. Rezultati: Vrijednost p< 0,05 postavljena je kao statistički značajna granica. Filtek™ Silorane može smanjiti otklon kvržica uzrokovan polimerizacijskom kontrakcijom, ali sumnja se može li se održati adhezivna veza. Zaključak: Premise™ Packable pokazao je veći otklon kvržica tijekom polimerizacije, ali i bolju adhezivnu vezu.Low shrinking resin composites are in the focus of research in posterior resin composite restoratives. In this context, the silorane-chemistry, incorporating ring-opening monomers and highly filled packable dimethacrylates seem to be most promising. Material and Methods: The goal of this study was to investigate cuspal deflection after light-curing in extracted upper premolars (n=10), using direct current differential transducers (DCDT), and adhesive interface integrity by scanning electron microscopy (SEM) evaluation, of two restorative systems: 1) Filtek™ Silorane/ Silorane System Adhesive (3M ESPE); 2) Premise™ Packable /OptiBond FL (KERR). Data were analysed using a two-tailed t-test. Results: A p-value < 0.05 was considered statistically significant. Filtek™ Silorane may reduce cuspal deflection associated to the polymerization process, but there is concern regarding durability of adhesive interface integrity. Conclusions: Premise™ Packable showed higher cuspal deflection and complete integrity of adhesive interface