439 research outputs found
The color dependent morphology of the post-AGB star HD161796
Context. Many protoplanetary nebulae show strong asymmetries in their
surrounding shell, pointing to asymmetries during the mass loss phase.
Questions concerning the origin and the onset of deviations from spherical
symmetry are important for our understanding of the evolution of these objects.
Here we focus on the circumstellar shell of the post-AGB star HD 161796. Aims.
We aim at detecting signatures of an aspherical outflow, as well as to derive
the properties of it. Methods. We use the imaging polarimeter ExPo (the extreme
polarimeter), a visitor instrument at the William Herschel Telescope, to
accurately image the dust shell surrounding HD 161796 in various wavelength
filters. Imaging polarimetry allows us to separate the faint, polarized, light
from circumstellar material from the bright, unpolarized, light from the
central star. Results. The shell around HD 161796 is highly aspherical. A clear
signature of an equatorial density enhancement can be seen. This structure is
optically thick at short wavelengths and changes its appearance to optically
thin at longer wavelengths. In the classification of the two different
appearances of planetary nebulae from HST images it changes from being
classified as DUPLEX at short wavelengths to SOLE at longer wavelengths. This
strengthens the interpretation that these two appearances are manifestations of
the same physical structure. Furthermore, we find that the central star is
hotter than often assumed and the relatively high observed reddening is due to
circumstellar rather than interstellar extinction.Comment: Accepted for publication in A&
Evolution annuelle du peuplement zooplanctonique dans un lagunage à haut rendement et incidence du temps de séjour
Proposé au début des années soixante par W.J. OSWALD, le lagunage dit « à haut rendement », utilisé pour l'épuration d'eaux usées domestiques, représente un écosystème hypereutrophe. Il se distingue considérablement du lagunage naturel par des temps de séjour très courts (2 à 12 jours), de très faibles profondeurs (< 1 m) et par une agitation constante de façon à favoriser le développement algal.Cette étude a pour objectifs de : 1) caractériser les successions saisonnières du zooplancton dans un écosystème où celles-ci n'ont pratiquement pas été étudiées et 2) étudier l'impact, sur la structure du peuplement et au fil des saisons, du temps de séjour des eaux à traiter.Le suivi du peuplement zooplanctonique a été réalisé pendant une période de deux ans dans deux bassins à haut rendement (nommés A et B) de même configuration alimentés en eaux usées. Les temps de résidence des eaux à traiter sont constants et de huit jours dans l'un, variable et ajusté selon l'ensoleillement et la charge entrante dans l'autre.Les résultats obtenus sont analysés par une classification hiérarchique avec contrainte de contiguïté temporelle. Les groupes obtenus sont ensuite testés par l'analyse discriminante. Les résultats sont regroupés chronologiquement : en six groupes pour le bassin B et en dix groupes pour le bassin A. L'analyse discriminante montre que les Crustacés et les Rotifères sont respectivement responsables des regroupements dans les bassins B et A. Pendant la période de démarrage du lagunage ainsi qu'en automne et en hiver, le zooplancton est principalement composé de Protozoaires : Ciliés libres ou fixés en fortes densités (jusqu'à 2,7.107 ind. 1-1) et Rhizopodes (Amibes). Au printemps et en été, lorsque le rayonnement solaire devient important, la production primaire étant optimale, les Protozoaires sont remplacés par des brouteurs herbivores métazoaires. La production de Rotifères et de Daphnies dont les exigences en nourriture (microalgues) sont considérables est importante au printemps ou bien en été uniquement dans le bassin à temps de séjour court. Le développement des Crustacés Copépodes et Ostracodes est favorisé en été dans le bassin à temps de séjour plus long.Tous ces organismes participent activement à réparation. ils se nourrissent pour la plupart en filtrant les éléments en suspension dans le milieu et participent directement à l'élimination des MES et de la DCO (PIZAY-PARENTY, 1985).II devient donc envisageable, par suite du rôle non négligeable joué par le zooplancton et surtout par Daphnia magna, de concevoir une gestion du lagunage qui favoriserait le développement de ce Cladocère. Cette biomasse facilement récupérable par tamisage peut être valorisée en aquaculture.High rate ponds for wastewater treatment have been the focus of much attention since their creation by W.J. OSWALD in the early 1960's. These aquatic ecosystems are hypereutrophic because of massive nutrient introduction by wastewater influents. These kinds of ponds are very different front natural biological ponds because of short residence times (2 to 12 days), shallow depths (<1 m) and constant mechanical mixing which improve alga : growth.This study presents the following objectives : 1) to characterize seasonal successions of zooplankton in this ecosystem where they are unknown and 2) to study residence time influence on zooplanktonic successions in function of seasons. Our investigation consists in studying two similar high rate ponds of 48 m2 surface area and 35 cm depth constantly stirred by paddle wheels.Only residence time is different. The first pond has eight days residence time and in the second one, it changes with solar radiations and organic matter concentrations. The influents come from a primary pond of eight days residence time, fed continuously with domestic influents front a small town, Mèze. The aim of this experiment is to compare seasonal successions in these two high rate ponds (called A and B) with different residence times. Zooplanktonic investigation has been carried out for two years. One sample was collected twice a week in primary pond effluent and two others samples collected once a week into the two high rate ponds near the outflow areas. The results of chronological clustering take inter account the discontinuities of zooplanktonic structure. We obtain six sequences in B pond and ten groups in A pond. Stepwise discriminant analysis shows that Crustaceans and Rotifers are respectively responsible for chronological clustering in B and in A pond. During the sterling period of wastewater treatment and in autumn and in winter, photosynthesis is low and zooplankton is composed mainly of Protozoa : free-living or fixed Ciliates in great concentrations (until 2,7.107 ind. l-1) and Rhizopods (Amæba sp.). These organisms have important food needs (bacteria and algal detritus). During spring and summer, as solar radiations become important, Protozoa are replaced by metazoan grazers. Spring or summer with short residence times increase Rotifers or Daphnia magna production white summer with longer residence times increase Cyclops sp and cypris ovum production. All these organisms are active components of wastewater treatment : the consumption of particulates by zooplankton Increases TSS and COD removal efficiencies (PIZAY-PARENTY, 1985).Therefore, because of the filtering activity of Crustaceans (especially of Daphnia magna), it seems possible to conceive a new pond managment, with residence time changes, favourable to exponential algal growth and consequently to crustacean biomass production. It is easier to harvest this biomass (with nets) than to harvest algal biomass, which still presents problems
Direct imaging of a massive dust cloud around R Coronae Borealis
We present recent polarimetric images of the highly variable star R CrB using
ExPo and archival WFPC2 images from the HST. We observed R CrB during its
current dramatic minimum where it decreased more than 9 mag due to the
formation of an obscuring dust cloud. Since the dust cloud is only in the
line-of-sight, it mimics a coronograph allowing the imaging of the star's
circumstellar environment. Our polarimetric observations surprisingly show
another scattering dust cloud at approximately 1.3" or 2000 AU from the star.
We find that to obtain a decrease in the stellar light of 9 mag and with 30% of
the light being reemitted at infrared wavelengths (from R CrB's SED) the grains
in R CrB's circumstellar environment must have a very low albedo of
approximately 0.07%. We show that the properties of the dust clouds formed
around R CrB are best fitted using a combination of two distinct populations of
grains size. The first are the extremely small 5 nm grains, formed in the low
density continuous wind, and the second population of large grains (~0.14
{\mu}m) which are found in the ejected dust clouds. The observed scattering
cloud, not only contains such large grains, but is exceptionally massive
compared to the average cloud.Comment: 8 pages, 7 figures published in A&
¿Cuál es la actitud de los médicos hacia el actual modelo de atención primaria?
ObjetivoDeterminar cómo es la actitud de los médicos hacia el actual modelo de atención primaria de salud y estimar su relación con variables de tipo sociodemográfico y/o laboral.DiseñoEstudio multicéntrico, transversal.EmplazamientoCentros de salud del Área II de la Región de Murcia.ParticipantesTotalidad de médicos generales, de familia y pediatras de los centros de salud mencionados (54 en total).Mediciones principalesComo instrumento de evaluación se utiliza la «Escala de actitudes hacia los contenidos de atención primaria de salud», de Ballesteros et al. Esta escala proporciona una puntuación total, así como una puntuación específica para cada una de las 7 dimensiones que la componen.ResultadosEn general, la actitud de los médicos es favorable (4,1 puntos de media sobre 5). En la dimensión «Inclusión de los profesionales del segundo nivel en atención primaria» es donde hemos encontrado una actitud menos favorable, siendo los médicos de familia los que se muestran más de acuerdo. En cuanto a las demás variables asociadas, los profesionales que trabajan en centros periféricos y en situación de interinidad muestran una actitud más positiva hacia el actual modelo.ConclusionesEl conocimiento de las actitudes de los profesionales, así como de las variables relacionadas, puede servir de base para diseñar posibles estrategias de intervención dirigidas a la mejora de la calidad asistencial en atención primaria y para una evolución positiva de los profesionales que prestan sus servicios.ObjectivesTo determine the attitude of doctors towards the current model of primary care and to calculate its relationship with social and demographic and/or work variables.DesignMulti-centre cross-sectional study.SettingHealth centres in Area II of the Murcia region.ParticipantsAll general practitioners, family doctors and paediatricians in the health centres mentioned (54 in all).Main measurementsThe «Scale of attitudes towards the contents of primary health care» by Ballesteros et al. was used as the tool of evaluation. This scale provides both a total score and a specific score for each of its 7 dimensions.ResultsIn general, doctors´ attitudes were favourable (4.1 points average out of 5). We found a less favourable attitude in the dimension «Inclusion of second-level professionals in primary care», with family doctors most in agreement. The professionals working in centres on the periphery and those without tenure had a more positive attitude towards the current model, for the remaining variables.ConclusionsUnderstanding professionals´ attitudes and the variables related to them may serve as a basis for designing intervention strategies aimed at improving the quality of primary care and for the positive evolution of professionals working in PC
Estudio de la regulación de la asparraginasa de pino
La asparraginasa (ASPG, EC 3.5.1.1) de plantas pertenece a la familia de Ntn-hidrolasas, enzimas que se sintetizan como un precursor inactivo, el cual es activado mediante un procesamiento autocatalítico que genera dos subunidades (α y β). Estas subunidades forman un tetrámero (αβ)2, que constituye la forma madura de la enzima, en la cual cada subunidad β presenta un residuo nucleófilo (Thr) en su extremo amino como resultado del procesamiento. La asparraginasa está implicada en la movilización del nitrógeno contenido en el grupo amido de la asparragina, el metabolito principal para la reserva y el transporte de nitrógeno en plantas. Nuestro objetivo es determinar cómo se regula esta enzima en pino, tanto a nivel transcripcional como postraduccional. A nivel transcripcional estamos realizando una caracterización estructural y funcional de la región promotora del gen, así como el análisis del patrón de expresión del gen en diferentes tejidos y condiciones. A nivel postraduccional nos hemos centrado en determinar las características del procesado y activación de la ASPG en pino. Debido a los bajos niveles de la proteína en pino, este estudio se abordó con proteína recombinante purificada desde sistemas heterólogos. La expresión de la proteína recombinante de Pinus pinaster en células de E. coli resulta en una proteína inmadura sin capacidad de autocatálisis in vitro, a diferencia de lo que se ha descrito para ASPG de otras especies angiospermas. Por el contrario, la expresión heteróloga en plantas de tabaco genera una proteína madura. En comparación con la estructura primaria de las ASPG de especies cuyo genoma ha sido secuenciado, las ASPG de coníferas presentan una extensión de unos 70 aminoácidos en la posición que precede al residuo nucleófilo, sitio donde ocurre el procesamiento que activa a la enzima. Un análisis mediante espectrometría de masas ha demostrado que esta extensión forma parte de la proteína de Pinus pinaster en su forma madura. En la actualidad estamos analizando el efecto de esta extensión sobre el autoprocesamiento del precursor.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
DZ Cha: a bona fide photoevaporating disc
DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright
protoplanetary disc with evidence of inner disc clearing. Its narrow \Ha line
and infrared spectral energy distribution suggest that DZ Cha may be a
photoevaporating disc. We aim to analyse the DZ Cha star + disc system to
identify the mechanism driving the evolution of this object. We have analysed
three epochs of high resolution optical spectroscopy, photometry from the UV up
to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry
observations of DZ Cha. Combining our analysis with previous studies we find no
signatures of accretion in the \Ha line profile in nine epochs covering a
time baseline of years. The optical spectra are dominated by
chromospheric emission lines, but they also show emission from the forbidden
lines [SII] 4068 and [OI] 6300 that indicate a disc outflow. The
polarized images reveal a dust depleted cavity of au in radius and two
spiral-like features, and we derive a disc dust mass limit of
M_\mathrm{dust}
80 \MJup) companions are detected down to 0\farcs07 ( au,
projected). The negligible accretion rate, small cavity, and forbidden line
emission strongly suggests that DZ Cha is currently at the initial stages of
disc clearing by photoevaporation. At this point the inner disc has drained and
the inner wall of the truncated outer disc is directly exposed to the stellar
radiation. We argue that other mechanisms like planet formation or binarity
cannot explain the observed properties of DZ Cha. The scarcity of objects like
this one is in line with the dispersal timescale ( yr) predicted
by this theory. DZ Cha is therefore an ideal target to study the initial stages
of photoevaporation.Comment: A&A in press, language corrections include
Exocomet signatures around the A-shell star Leo?
We present an intensive monitoring of high-resolution spectra of the Ca {\sc
ii} K line in the A7IV shell star Leo at very short (minutes, hours),
short (night to night), and medium (weeks, months) timescales. The spectra show
remarkable variable absorptions on timescales of hours, days, and months. The
characteristics of these sporadic events are very similar to most that are
observed toward the debris disk host star Pic, which are commonly
interpreted as signs of the evaporation of solid, comet-like bodies grazing or
falling onto the star. Therefore, our results suggest the presence of solid
bodies around Leo. To our knowledge, with the exception of Pic,
our monitoring has the best time resolution at the mentioned timescales for a
star with events attributed to exocomets. Assuming the cometary scenario and
considering the timescales of our monitoring, our results indicate that
Leo presents the richest environment with comet-like events known to date,
second only to Pic.Comment: A&A letters, proof-correcte
Aspectos estructurales y funcionales de la asparraginasa en pino
La asparragina es un metabolito clave en plantas para el transporte y reserva temporal de nitrógeno. La principal vía de movilización del nitrógeno contenido en el grupo amido de este aminoácido implica a la enzima asparraginasa (ASPG, EC 3.5.1.1), que cataliza la hidrólisis de asparragina a aspartato y amonio. Las asparraginasas de plantas, al igual que todas las enzimas de la familia Ntn-hidrolasas, son sintetizadas como precursores inactivos. La enzima activa es un heterotetrámero con dos tipos distintos de angiospermas se han identificado genes que codifican dos subtipos de asparraginasas (Bruneau et al. 2006), las K+-independientes y las K+-dependientes, con al menos un gen codificante para cada tipo en los genomas que han sido secuenciados. La caracterización de ambos subtipos indica que la forma K+-dependiente sería más eficiente en la movilización del nitrógeno amido de la asparragina bajo condiciones de alta demanda metabólica de nitrógeno (Bruneau et al. 2006), mientras que el papel de las K+-independientes estaría relacionado con su actividad isoaspartil dipeptidasa. Sin embargo, hasta la fecha no se ha realizado una caracterización de las distintas formas presentes y sus funciones en gimnospermas. Una búsqueda en el transcriptoma disponible de Pinus pinaster (Canales et al. 2014) nos permitió identificar un total de tres genes con similitud a asparraginasa. Sólo uno (PpASPG1), identificado previamente por nuestro grupo de investigación (Cañas et al. 2006), presenta mayor similitud con las asparraginasas K+-dependientes. El principal inconveniente para la caracterización de estas proteínas es su baja abundancia. Para soslayar este impedimento se expresaron transitoriamente los tres genes de pino en un sistema heterólogo, se purificaron las proteínas recombinantes y se compararon sus características. Por otro lado, esta aproximación nos ha permitido también estudiar cómo afecta al procesamiento del precursor y a la actividad de la enzima la presencia de una extensión de 70 aminoácidos proteínas ortólogas de especies angiospermas. Finalmente, con el objetivo de dilucidar posibles funciones, hemos realizado un análisis de expresión de los tres genes identificados, así como el aislamiento y análisis del promotor del gen PpASPG1.
Referencias
Bruneau L. et al (2006) Co-occurrence of both L-asparaginase subtypes in Arabidopsis: At3g16150 encodes a K+-dependent L-asparaginase. Planta, 224:668–679, doi: 10.1007/s00425-006-0245-9.
Canales J. et al. (2014) De novo assembly of maritime pine transcriptome: implications for forest breeding and biotechnology. Plant Biotechnology Journal, 12:286–299. doi: 10.1111/pbi.12136.
Cañas RA et al. (2006) Coordination of PsAS1 and PsASPG expression controls timing of re-allocated N utilization in hypocotyls of pine seedlings. Planta, 225:1205– 1219. doi: 10.1007/s00425-006-0431-9.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Surprising detection of an equatorial dust lane on the AGB star IRC+10216
Understanding the formation of planetary nebulae remains elusive because in
the preceding asymtotic giant branch (AGB) phase these stars are heavily
enshrouded in an optically thick dusty envelope. To further understand the
morphology of the circumstellar environments of AGB stars we observe the
closest carbon-rich AGB star IRC+10216 in scattered light. When imaged in
scattered light at optical wavelengths, IRC+10216 surprisingly shows a narrow
equatorial density enhancement, in contrast to the large-scale spherical rings
that have been imaged much further out. We use radiative transfer models to
interpret this structure in terms of two models: firstly, an equatorial density
enhancement, commonly observed in the more evolved post-AGB stars, and
secondly, in terms of a dust rings model, where a local enhancement of
mass-loss creates a spiral ring as the star rotates. We conclude that both
models can be used to reproduce the dark lane in the scattered light images,
which is caused by an equatorially density enhancement formed by dense dust
rather than a bipolar outflow as previously thought. We are unable to place
constraints on the formation of the equatorial density enhancement by a binary
system.Comment: 9 pages, 4 figure
The atypical CDK activator RingoA/Spy1 regulates exit from quiescence in neural stem cells
In the adult mammalian brain, most neural stem cells (NSCs) are held in a reversible state of quiescence, which is essential to avoid NSC exhaustion and determine the appropriate neurogenesis rate. NSCs of the mouse adult subependymal niche provide neurons for olfactory circuits and can be found at different depths of quiescence, but very little is known on how their quiescence-to-activation transition is controlled. Here, we identify the atypical cyclin-dependent kinase (CDK) activator RingoA as a regulator of this process. We show that the expression of RingoA increases the levels of CDK activity and facilitates cell cycle entry of a subset of NSCs that divide slowly. Accordingly, RingoA-deficient mice exhibit reduced olfactory neurogenesis with an accumulation of quiescent NSCs. Our results indicate that RingoA plays an important role in setting the threshold of CDK activity required for adult NSCs to exit quiescence and may represent a dormancy regulator in adult mammalian tissues.© 2023 The Author(s)
- …