Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph -- III. Dust Grains in Young L Dwarf Atmospheres Are Heavier

Analysis of all archival 5--14 micron spectra of field ultracool dwarfs from the Infrared Spectrograph on the Spitzer Space Telescope has shown that absorption by silicates in the 8--11 micron region is seen in most L-type (1300 K to 2200 K) dwarfs. The absorption is caused by silicate-rich clouds in the atmospheres of L dwarfs and is strongest at L4--L6 spectral types. Herein we compare averages of the mid-infrared silicate absorption signatures of L3--L7 dwarfs that have low ($\lesssim$10$^{4.5}$ cm s$^{-2}$) vs.\ high ($\gtrsim$10$^5$ cm s$^{-2}$) surface gravity. We find that the silicate absorption feature is sensitive to surface gravity and indicates a difference in grain size and composition between dust condensates in young and old mid-L dwarfs. The mean silicate absorption profile of low-gravity mid-L dwarfs matches expectations for $\sim$1 micron-sized amorphous iron- and magnesium-bearing pyroxene (Mg$_x$Fe$_{1-x}$SiO$_3$) grains. High-gravity mid-L dwarfs have silicate absorption better represented by smaller ($\lesssim$0.1 $\mu$m) and more volatile amorphous enstatite (MgSiO$_3$) or SiO grains. This is the first direct spectroscopic evidence for gravity-dependent sedimentation of dust condensates in ultracool atmospheres. It confirms theoretical expectations for lower sedimentation efficiencies in low-gravity atmospheres and independently confirms their increased dustiness.Comment: Accepted for publication in MNRA

Learning difficulties among students when applying Ampére-Maxwell’s law and its implications for teaching

We investigate learning difficulties among second-year students in electromagnetism courses when they apply Ampére-Maxwell’s law. Using phenomenography, we analyzed written answers from 65 undergraduate physics students to four questions on Ampére’s and Ampére-Maxwell’s laws. We complemented our research by interviewing 12 students. To design the questionnaire, we ran an epistemological analysis of classical electromagnetism which helped us to identify a set of key essential concepts to understand this theory, guided the definition of learning objectives, and drew up the questions. The results revealed that the students found it hard to recognize the validity framework from Ampére’s law and to apply AmpéreMaxwell’s law. They face particular difficulties to recognize the appearance of the displacement current and the relationship between the circulation of the magnetic field and an electric field that is variable over time.ANII: POS_NAC_2023_5_17767

Students’ conceptual difficulties in hydrodynamics

We describe a study on the conceptual difficulties faced by college students in understanding hydrodynamics of ideal fluids. This study was based on responses obtained in hundreds of written exams complemented with several oral interviews, which were held with first-year engineering and science university students. Their responses allowed us to identify a series of misconceptions unreported in the literature so far. The study findings demonstrate that the most critical difficulties arise from the students’ inability to establish a link between the kinematics and dynamics of moving fluids, and from a lack of understanding regarding how different regions of a system interact

Atmospheric Waves Driving Variability and Cloud Modulation on a Planetary-Mass Object

Planetary-mass objects and brown dwarfs at the transition ($\rm{T}_{eff}\sim1300$\,K) from relatively red L dwarfs to bluer mid-T dwarfs show enhanced spectrophotometric variability. Multi-epoch observations support atmospheric planetary-scale (Kelvin or Rossby) waves as the primary source of this variability; however, large spots associated with the precipitation of silicate and metal clouds have also been theorized and suggested by Doppler imaging. We applied both wave and spotted models to fit near-infrared (NIR), multi-band ($Y$/$J$/$H$/$K$) photometry of SIMP\,J013656.5+093347 (hereafter SIMP0136), collected at the Canada-France-Hawaii Telescope using the Wide-field InfraRed Camera. SIMP0136 is a planetary-mass object (12.7$\pm1.0 \ \rm{M_J}$) at the L/T transition (T2$\pm0.5$) known to exhibit light curve evolution over multiple rotational periods. We measure the maximum peak-to-peak variability of $6.17\pm0.46\%$, $6.45\pm0.33\%$, $6.51\pm0.42\%$, and $4.33\pm0.38\%$ in the $Y$, $J$, $H$, and $K$ bands respectively, and find evidence that wave models are preferred for all four NIR bands. Furthermore, we determine the spot size necessary to reproduce the observed variations is larger than the Rossby deformation radius and Rhines scale, which is unphysical. Through the correlation between light curves produced by the waves and associated color variability, we find evidence of planetary-scale, wave-induced cloud modulation and breakup, similar to Jupiter's atmosphere and supported by general circulation models. We also detect a $93.8^{\circ}\pm7.4^{\circ}$ ($12.7\sigma$) phase shift between the $H-K$ and $J-H$ color time series, providing evidence for complex vertical cloud structure in SIMP0136's atmosphere.Comment: 22 pages, 10 figures, 3 tables. Accepted for publication in Ap

Close companions around young stars

Multiplicity is a fundamental property that is set early during stellar lifetimes, and it is a stringent probe of the physics of star formation. The distribution of close companions around young stars is still poorly constrained by observations. We present an analysis of stellar multiplicity derived from APOGEE-2 spectra obtained in targeted observations of nearby star-forming regions. This is the largest homogeneously observed sample of high-resolution spectra of young stars. We developed an autonomous method to identify double lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass range of $\sim$0.05--1.5 \msun, we find 399 binaries, including both RV variables and SB2s. The mass ratio distribution of SB2s is consistent with a uniform for $q0.95$. The period distribution is consistent with what has been observed in close binaries ($<10$ AU) in the evolved populations. Three systems are found to have $q\sim$0.1, with a companion located within the brown dwarf desert. There are not any strong trends in the multiplicity fraction (MF) as a function of cluster age from 1 to 100 Myr. There is a weak dependence on stellar density, with companions being most numerous at $\Sigma_*\sim30$ stars/pc$^{-2}$, and decreasing in more diffuse regions. Finally, disk-bearing sources are deficient in SB2s (but not RV variables) by a factor of $\sim$2; this deficit is recovered by the systems without disks. This may indicate a quick dispersal of disk material in short-period equal mass systems that is less effective in binaries with lower $q$.Comment: 25 pages, 20 figures. Accepted to A

La violencia: Signos y expresiones del espacio urbano del puerto veracruzano.

En algunas ciudades latinoamericanas (Ciudad Juárez, Sao Paulo, Río de Janeiro, Medellín, San Salvador, entre otras) el crimen organizado protagoniza cotidianamente actos de extrema violencia y crueldad, lo que sin duda parece estar redefiniendo el espacio público urbano, por lo tanto, las formas de habitar las ciudades de hoy y sus formas de enunciación, se han transformado considerablemente. El paisaje citadino se ha transformado: otros actores sociales, otras narrativas y otras maneras de entender la vida en la urbanidad van redefiniendo todos los días la experiencia ciudadana. Aquí los medios de comunicación junto al Internet juegan un papel preponderante por la forma en que tratan el acontecimiento así como por la manera en que el crimen organizado ha generado sus propias fórmulas de visibilidad. Todo esto es analizado a la luz del incremento en la violencia urbana y el narcotráfico que se ha vivido en Veracruz y su conurbación en los últimos años. AbstractThe violence that in the latianoamerican cities (Ciudad Juárez, Sao Paulo, Río de Janeiro, Medellín, San Salvador, among others) heads the organized crime, seems has come redefining the urban public space, therefore the forms to inhabit the cities of today and their forms of enunciation. The citadino landscape has become: other social actors, other narratives and other ways to understand the life in the large city are redefining the citizen experience. Here the mass media next to the Internet play a preponderant role by the form in which they treat the event as well as by the way in which the organized crime has generated its own formulas of visibility. All this is analyzed in the light of the increase in the urban violence and the drug trafficking has lived in Veracruz and its conurbation in the last years

Tratamiento previo a la tintura, para estabilizar el elastano y evitar quiebres en la tela de punto (91%) algodón (9%) elastano mediante proceso húmedo

Establecer un tratamiento previo a la tintura, para estabilizar el elastano y evitar quiebres en la tela de punto (91%) Algodón – (9%) elastano mediante proceso húmedo.Los quiebres en el tejido de punto algodón ¿ elastano que se producen en el proceso de tintura, provocan que la tela con esta falla sea destinada como, tela de segunda calidad. El aumento de la tela de segunda calidad ocasiona pérdidas económicas a la empresa. Empresas ¿Pinto S.A.¿ fue creada en el año 1913, tiene como actividad la confección de prendas de vestir con telas de tejido plano y de punto, las telas de tejido plano compra a terceros, en cuanto para la elaboración de tejido de punto, cuenta con una fábrica que está compuesta por un área de tejeduría y otra de tintorería y acabados, en esta se realiza varios tipos de tejidos como, jersey, pique, fleece, acanalados y variaciones de estos tipos con Elastano. Para eliminar los quiebres en la tela jersey elastano 40 denier 1-1 H30/1 pima, que es el objeto de estudio, anteriormente se lo hacía en una máquina termofijadora antigua que no contaba con los respectivos sensores para controlar los parámetros del proceso, era una adaptación para satisfacer las necesidades de la empresa, pero la verdad no llenaba las expectativas, ya que no eliminaba totalmente los quiebres y provocaba el aparecimiento de doble tonalidad, dobleces a lo largo del tejido tubular procesado, y por esta razón se suspendió su uso. La tela de punto algodón - Elastano al no ser termofijada aumento de forma notable el aparecimiento de quiebres en su estructura, por esta razón se ha visto la necesidad de encontrar una alternativa para eliminar este problema.Ingenierí