308 research outputs found
On the Impact of Neutron Star Binaries Natal-Kick Distribution on the Galactic r-process Enrichment
We study the impact of the neutron star binaries' (NSBs) natal kick
distribution on the Galactic r-process enrichment. We model the growth of a
Milky Way type halo based on N-body simulation results and its star formation
history based on multi epoch abundance matching techniques. We consider the
NSBs that merge well beyond the galaxy's effective radius () do not contribute to Galactic r-process enrichment. Assuming a
power-law delay-time distribution (DTD) function () with
Myr for binaries' coalescence timescales, and an
exponential profile for their natal kick distribution with an average value of
180 km s, we show that up to 40% of all formed NSBs do not
contribute to r-process enrichment by , either because they merge far from
the galaxy at a given redshift (up to 25%) or have not yet merged by
today (15%). Our result is largely insensitive to the details of the DTD
function. Assuming a constant coalescence timescale of 100 Myr well
approximates the adopted DTD with 30% of the NSBs not contributing to r-process
enrichment. Our results, although rather dependent on the adopted natal kick
distribution, represent a first step towards estimating the impact of natal
kicks and DTD functions on r-process enrichment of galaxies that would need to
be incorporated in the hydrodynamical simulations.Comment: 7 pages, 3 figures, MNRAS Accepte
Following the Cosmic Evolution of Pristine Gas III: The Observational Consequences of the Unknown Properties of Population III Stars
We study the observational consequences of several unknown properties of
Population III (Pop III) stars using large-scale cosmological simulations that
include a subgrid model to track the unresolved mixing of pollutants. Varying
the value of the critical metallicity that marks the boundary between Pop III
and Population II (Pop II) star formation across 2 dex has a negligible effect
on the fraction of Pop III stars formed and the subsequent fraction of Pop III
flux from high-redshift galaxies. However, adopting a log normal initial mass
function (IMF) for Pop III stars, in place of a baseline Salpeter IMF, results
in a Pop III star formation rate density (SFRD) that is 1/4 of the baseline
rate. The flux from high-redshift galaxies modeled with this IMF is highly
bimodal, resulting in a tiny fraction of galaxies with more than
75\% of their flux coming from Pop III stars. However, at , right before
reionization in our simulations, 20\% of galaxies are Pop III-bright
with mag and at least 75\% of their flux generated by Pop
III stars . Additionally, the log normal Pop III IMF results in a population of
carbon enhanced, metal poor stars in reasonable agreement with MW halo
observations. Our analysis supports the conclusion that the Pop III IMF was
dominated by stars in the 20-120 range that generate SN with
carbon-enhanced ejecta.Comment: Accepted by Ap
Les relations entre communautés linguistiques en contexte scolaire et communautaire : regards croisés sur Montréal et Bruxelles
Lâobjectif de cet article est de prĂ©senter et de comparer le rĂŽle des milieux communautaires et scolaires dans les rapports entre communautĂ©s linguistiques historiques de MontrĂ©al et de Bruxelles. MĂȘme si ces deux contextes linguistiques sont diffĂ©rents Ă bien des Ă©gards, ils partagent deux caractĂ©ristiques qui laissent croire que lâune et lâautre des communautĂ©s puissent apprendre de lâexpĂ©rience quâelles ont dĂ©veloppĂ©e en parallĂšle, soit : un contexte dâambiguĂŻtĂ© de dominance ethnique et un systĂšme scolaire divisĂ© linguistiquement. Sur base de recherches rĂ©centes, nous ferons le bilan de lâĂ©tat des rapports dans les milieux scolaires et communautaires entre francophones et anglophones montrĂ©alais dâune part (PagĂ© et al. 2007, CĂŽtĂ© 2005) et entre jeunes francophones et nĂ©erlandophones Ă Bruxelles dâautre part (Mettewie 2004, Janssens et Van Mensel 2006). Lâimpact de ce contact intercommunautaire sur les reprĂ©sentations et les attitudes fera Ă©merger, en conclusion, des questions qui, Ă la lecture de ces deux contextes, induisent des pistes de recherches complĂ©mentaires et comparatives.The objective of this article is to present and compare the role of community and school milieus through relationships between the historical linguistic communities of MontrĂ©al and Brussels. Although these two linguistic contexts differ in many ways, they share two characteristics, which suggest that each of these communities could learn from the experience they developed in parallel â a context of the ambiguity of ethnic dominance and a linguistically divided school system. On the basis of recent research, we will examine the connections in the school and community milieus between French- and English-speaking MontrĂ©alers (PagĂ© et al. 2007, CĂŽtĂ© 2005) and between young French-speaking and Dutch-speaking students (Mettewie 2004, Janssens and Van Mensel 2006). In conclusion, the impact this intercommunity contact has on representations and attitudes brings out questions which, in examining these two contexts, reveals possibilities for complimentary and comparative research.El objetivo de este artĂculo es presentar y comparar el rol de los medios comunitarios y escolares en las relaciones entre comunidades lingĂŒĂsticas histĂłricas en Montreal y en Bruselas. Aunque dichos contextos lingĂŒĂsticos difieran en muchos aspectos, comparten dos caracterĂsticas que permiten pensar que ambas comunidades puedan aprender de la experiencia que de manera paralela han vivido, es decir: un contexto de ambigĂŒedad en el campo Ă©tnico y un sistema escolar lingĂŒĂsticamente dividido. BasĂĄndonos en investigaciones recientes, realizaremos un balance de las relaciones en el medio escolar y comunitario entre francĂłfonos y anglĂłfonos en Montreal (PagĂ© et al, 2007; CotĂ© 2005) y entre los jĂłvenes francĂłfonos y neerlandeses en Bruselas (Mattewie 2004; Janssens y Van Mensel 2006). El impacto del contacto Ănter-comunitario sobre las representaciones y las actitudes mostrarĂĄ, en conclusiĂłn, cuestiones que de acuerdo con la lectura de dichos contextos, sugieren pistas complementarias y comparativas de investigaciĂłn
SYGMA: Stellar Yields for Galactic Modeling Applications
The stellar yields for galactic modeling applications (SYGMA) code is an
open-source module that models the chemical ejecta and feedback of simple
stellar populations (SSPs). It is intended for use in hydrodynamical
simulations and semi-analytic models of galactic chemical evolution. The module
includes the enrichment from asymptotic giant branch (AGB) stars, massive
stars, SNIa and neutron-star mergers. An extensive and extendable stellar
yields library includes the NuGrid yields with all elements and many isotopes
up to Bi. Stellar feedback from mechanic and frequency-dependent radiative
luminosities are computed based on NuGrid stellar models and their synthetic
spectra. The module further allows for customizable initial-mass functions and
supernova Ia (SNIa) delay-time distributions to calculate time-dependent ejecta
based on stellar yield input. A variety of r-process sites can be included. A
comparison of SSP ejecta based on NuGrid yields with those from Portinari et
al. (1998) and Marigo (2001) reveals up to a factor of 3.5 and 4.8 less C and N
enrichment from AGB stars at low metallicity, a result we attribute to NuGrid's
modeling of hot-bottom burning. Different core-collapse supernova explosion and
fallback prescriptions may lead to substantial variations for the accumulated
ejecta of C, O and Si in the first at . An online
interface of the open-source SYGMA module enables interactive simulations,
analysis and data extraction of the evolution of all species formed by the
evolution of simple stellar populations.Comment: 18 pages, 10 figures, 3 tables, published in ApJ
Validating Semi-Analytic Models of High-Redshift Galaxy Formation using Radiation Hydrodynamical Simulations
We use a cosmological hydrodynamic simulation calculated with Enzo and the
semi-analytic galaxy formation model (SAM) GAMMA to address the chemical
evolution of dwarf galaxies in the early universe. The long-term goal of the
project is to better understand the origin of metal-poor stars and the
formation of dwarf galaxies and the Milky Way halo by cross-validating these
theoretical approaches. We combine GAMMA with the merger tree of the most
massive galaxy found in the hydrodynamic simulation and compare the star
formation rate, the metallicity distribution function (MDF), and the
age-metallicity relationship predicted by the two approaches. We found that the
SAM can reproduce the global trends of the hydrodynamic simulation. However,
there are degeneracies between the model parameters and more constraints (e.g.,
star formation efficiency, gas flows) need to be extracted from the simulation
to isolate the correct semi-analytic solution. Stochastic processes such as
bursty star formation histories and star formation triggered by supernova
explosions cannot be reproduced by the current version of GAMMA. Non-uniform
mixing in the galaxy's interstellar medium, coming primarily from
self-enrichment by local supernovae, causes a broadening in the MDF that can be
emulated in the SAM by convolving its predicted MDF with a Gaussian function
having a standard deviation of ~0.2 dex. We found that the most massive galaxy
in the simulation retains nearby 100% of its baryonic mass within its virial
radius, which is in agreement with what is needed in GAMMA to reproduce the
global trends of the simulation.Comment: 26 pages, 13 figures, 2 tables, submitted to ApJ (version 2
ModĂšle dâĂ©volution de galaxies pour simulations cosmologiques Ă grande Ă©chelle
Tableau d'honneur de la FacultĂ© des Ă©tudes supĂ©rieures et postdorales, 2014-2015Nous prĂ©sentons un modĂšle semi-analytique (MSA) conçu pour ĂȘtre utilisĂ© dans une simulation hydrodynamique Ă grande Ă©chelle comme traitement de sous-grille afin de gĂ©nĂ©rer lâĂ©volution des galaxies dans un contexte cosmologique. Le but ultime de ce projet est dâĂ©tudier lâhistoire de lâenrichissement chimique du milieu intergalactique (MIG) ainsi que les interactions entre les galaxies et leur environnement. Le MSA inclut tous les ingrĂ©dients nĂ©cessaires pour reproduire lâĂ©volution des galaxies de faible masse et de masse intermĂ©diaire. Cela comprend lâaccrĂ©tion du halo galactique et du MIG, le refroidissement radiatif, la formation stellaire, lâenrichissement chimique et la production de vents galactiques propulsĂ©s par lâĂ©nergie mĂ©canique et la radiation des Ă©toiles massives. La physique des bulles interstellaires est appliquĂ©e Ă chaque population dâĂ©toiles qui se forme dans le modĂšle afin de relier lâactivitĂ© stellaire Ă la production des vents galactiques propulsĂ©s par lâĂ©nergie mĂ©canique. Nous utilisons des modĂšles stellaires Ă jour pour gĂ©nĂ©rer lâĂ©volution de chacune des populations dâĂ©toiles en fonction de leur masse, de leur mĂ©tallicitĂ© et de leur Ăąge. Cela permet dâinclure, dans le processus dâenrichissement, les vents stellaires des Ă©toiles massives, les supernovae de Type II, Ib et Ic, les hypernovae, les vents stellaires des Ă©toiles de faible masse et de masse intermĂ©diaire ainsi que les supernovae de Type Ia. Avec ces ingrĂ©dients, notre modĂšle peut reproduire les abondances de plusieurs Ă©lĂ©ments observĂ©es dans les Ă©toiles du voisinage solaire. De maniĂšre plus gĂ©nĂ©rale, notre MSA peut reproduire la relation actuelle observĂ©e entre la masse stellaire des galaxies et la masse de leur halo de matiĂšre sombre. Il peut aussi reproduire la mĂ©tallicitĂ©, la quantitĂ© dâhydrogĂšne et le taux de formation stellaire spĂ©cifique observĂ©s dans les galaxies de lâUnivers local. Notre modĂšle est Ă©galement consistant avec les observations suggĂ©rant que les galaxies de faible masse sont davantage affectĂ©es par la rĂ©troaction stellaire que les galaxies plus massives. De plus, le modĂšle peut reproduire les diffĂ©rents comportements, soit oscillatoire ou stable, observĂ©s dans lâĂ©volution du taux de formation stellaire des galaxies. Tous ces rĂ©sultats dĂ©montrent que notre MSA est suffisamment qualifiĂ© pour traiter lâĂ©volution des galaxies Ă lâintĂ©rieur dâune simulation cosmologique.We present a semi-analytical model (SAM) designed to be used in a large-scale hydrodynamical simulation as a sub-grid treatment in order to generate the evolution of galaxies in a cosmological context. The ultimate goal of this project is to study the chemical enrichment history of the intergalactic medium (IGM) and the interactions between galaxies and their surrounding. Presently, the SAM takes into account all the ingredients needed to compute the evolution of low- and intermediate-mass galaxies. This includes the accretion of the galactic halo and the IGM, radiative cooling, star formation, chemical enrichment, and the production of galactic outflows driven by the mechanical energy and the radiation of massive stars. The physics of interstellar bubbles is applied to every stellar population which forms in the model in order to link the stellar activity to the production of outflows driven by mechanical energy. We use up-to-date stellar models to generate the evolution of each stellar population as a function of their mass, metallicity, and age. This enables us to include, in the enrichment process, the stellar winds from massive stars, Type II, Ib, and Ic supernovae, hypernovae, the stellar winds from low- and intermediate-mass stars in the asymptotic giant branch, and Type Ia supernovae. With these ingredients, our model can reproduce the abundances of several elements observed in the stars located in the solar neighborhood. More generally, our SAM reproduces the current stellar-to-dark-halo mass relation observed in galaxies. It can also reproduce the metallicity, the hydrogen mass fraction, and the specific star formation rate observed in galaxies as a function of their stellar mass. Our model is also consistent with observations which suggest that low-mass galaxies are more affected by stellar feedback than higher-mass galaxies. Moreover, the model can reproduce the periodic and the stable behaviors observed in the star formation rate of galaxies. All these results show that our SAM is sufficiently qualified to treat the evolution of low- and intermediate-mass galaxies inside a large-scale cosmological simulation
Les figures de lâintimitĂ© en situation de rue : une pluralitĂ© dâexpĂ©riences chez les jeunes Ă MontrĂ©al
Cette Ă©tude a pour objectif de comprendre les significations que les jeunes en situation de rue Ă MontrĂ©al accordent Ă leurs relations intimes. Si la plupart des travaux empiriques misent essentiellement sur les risques que prĂ©sentent les activitĂ©s sexuelles pour la santĂ© des jeunes en situation de rue, peu dâentre eux tentent de comprendre, Ă partir du point de vue des jeunes eux-mĂȘmes, le sens quâils donnent Ă leurs relations intimes. Câest Ă la lumiĂšre de ces travaux que cette Ă©tude propose de dĂ©passer une lecture rĂ©ductrice de lâintimitĂ© de ces jeunes en apprĂ©hendant lâarticulation entre leurs expĂ©riences intimes et leurs expĂ©riences de rue.
InspirĂ©e de la sociologie de lâexpĂ©rience de Dubet (1994), cette Ă©tude sâintĂ©resse Ă la construction de lâexpĂ©rience intime des jeunes en situation de rue dans un rapport dynamique entre leur espace dâautonomie et les conditions sociales qui les encadrent. Ce cadre dâanalyse permet de rompre avec les travaux qui prĂ©sentent ces jeunes soit comme des victimes passives des conditions de vie prĂ©caires de la situation de rue, soit comme des ĂȘtres imprudents ou insouciants en matiĂšre de sexualitĂ©. Sâinscrivant dans une mĂ©thodologie qualitative, des entrevues individuelles ont Ă©tĂ© rĂ©alisĂ©es auprĂšs de trente-deux jeunes en situation de rue (18 femmes et 14 hommes) ĂągĂ©s de 18 Ă 27 ans (moyenne = 22 ans). Les tĂ©moignages de ces jeunes ont Ă©tĂ© analysĂ©s Ă partir dâune mĂ©thode typologique (Schnapper, 2005) qui a permis dâĂ©laborer des types-idĂ©aux dâexpĂ©riences intimes en situation de rue, les « figures de lâintimitĂ© ».
Lâanalyse des tĂ©moignages a permis de dĂ©gager cinq figures de lâintimitĂ© en situation de rue: la rĂ©ussite criminelle, le retrait, la survie, lâengagement et lâenfermement. Si chacune de ces figures propose des articulations singuliĂšres entre les expĂ©riences intimes et les expĂ©riences de rue des jeunes Ă MontrĂ©al, cette analyse permet nĂ©anmoins de soulever des recoupements thĂ©oriques entre les types-idĂ©aux identifiĂ©s dans cette Ă©tude. Il est possible de constater que les jeunes des figures de la rĂ©ussite criminelle et de lâengagement tissent une expĂ©rience intĂ©grĂ©e de la situation de rue par la construction dâun sentiment dâappartenance Ă un groupe de pairs, tandis que ceux des figures du retrait et de la survie tĂ©moignent dâune expĂ©rience de rejet oĂč la situation de rue est considĂ©rĂ©e comme disqualifiante. Ăgalement, lâanalyse des tĂ©moignages illustre que les jeunes des figures du retrait et de lâengagement rapportent une subjectivation des partenaires intimes par un engagement affectif et Ă©motionnel, tandis que ceux des figures de la rĂ©ussite criminelle et de la survie dĂ©crivent une objectivation de la sexualitĂ© pour rĂ©pondre Ă diffĂ©rents besoins. Cette Ă©tude met donc en lumiĂšre lâimportance dâapprĂ©hender lâarticulation entre les relations intimes des jeunes et le rapport quâils entretiennent Ă lâĂ©gard de la situation de rue afin de saisir la pluralitĂ© et la complexitĂ© de leurs expĂ©riences de vie.The objective of this study is to understand how street-involved youth in Montreal experience their intimate relationships. Most studies focused on sexual health and HIV infection risks. However, little is known about the meanings they give to their intimate relationships and how they are influenced by the street life. In this study, the relationship between intimate experiences and street experiences of young street-involved people is explored.
Inspired by the sociology of experience (Dubet, 1994), this study focuses on the construction of the intimate experience of street-involved youth, assuming a dynamic relationship between their agency and the social and material conditions of the street life. This analytical framework allows us to overcome the empirical works which present these youth as passive victims of precarious living conditions or as careless and reckless when it comes to sexuality. Individual interviews were conducted with thirty-two street-involved youth (18 women and 14 men) aged from 18 to 27 years old (mean = 22 years old). The testimonies were analyzed within a qualitative typological framework (Schnapper, 2005), allowing the construction of ideal types of intimate experiences in the street life, the âfigures of intimacyâ.
Five figures of intimacy in the street life among young people were constructed based on the testimonies analysis: criminal success, withdrawal, survival, commitment and confinement. Each of these figures offers a unique dynamic description between intimate experiences and street experiences of the participants. The analysis shows some overlaps between the figures. Youth from the criminal success and the commitment figures build a sense of belonging to a peer group in the street situation, while youth from the withdrawal and survival figures perceived the street situation as disqualifying and try to stay away from other street-involved young people. Also, participants from the criminal success and survival figures reported a subjectivation of the intimate partner through emotional commitment. In contrast, youth in the withdrawal and the commitment figures showed a tendency to instrumentalize sexuality in order to satisfy various needs. This study illustrates the importance of understanding the dynamic between intimate relationships and the street life to capture the diversity and the complexity of the life experiences of the street-involved young people
Une démarche d'évaluation formative et qualitative de l'implantation du programme d'éducation sexuelle "à grands pas d'amour" s'adressant à des adolescents de sexe masculin résidant en centre jeunesse
En 2004, le programme d'Ă©ducation sexuelle Ă grands pas d'amour (APA) a Ă©tĂ© dĂ©veloppĂ© et implantĂ© pour les garçons rĂ©sidant en Centre jeunesse. Bien que plusieurs chercheurs suggĂšrent de dĂ©velopper des interventions en matiĂšre de sexualitĂ© spĂ©cifiques pour les adolescents de sexe masculin, peu de travaux empiriques fournissent une Ă©valuation de ces programmes. La majoritĂ© de ces Ă©valuations ont Ă©tĂ© rĂ©alisĂ©es en fonction de l'efficacitĂ© des interventions, mais presque aucune d'entre elles ne procurent des informations sur leur mise en Ćuvre. C'est dans le but de dĂ©crire la mise en application du programme APA, afin de le bonifier pour les prochaines annĂ©es, que la prĂ©sente Ă©tude porte sur une dĂ©marche d'Ă©valuation formative de son implantation. Les donnĂ©es ont Ă©tĂ© recueillies en utilisant une mĂ©thodologie qualitative inspirĂ©e du modĂšle d'Ă©valuation pluraliste-constructiviste de Guba et Lincoln (1989). Vingt adolescents ayant participĂ© au programme ont Ă©tĂ© interviewĂ©s dans le cadre d'entrevues individuelles et vingt-neuf ont rĂ©pondu Ă un questionnaire dirigĂ©. De plus, treize Ă©ducateurs ayant dispensĂ© le programme ont rempli un questionnaire dirigĂ© et semi-dirigĂ©. Des notes manuscrites ont Ă©galement Ă©tĂ© prises lors de rencontres de supervision auprĂšs de ces mĂȘmes intervenants. Les rĂ©sultats montrent que le programme a suscitĂ© un intĂ©rĂȘt et un engouement qui ont permis de crĂ©er un rapprochement entre les jeunes et les Ă©ducateurs. Ces constats font ressortir l'importance de promouvoir un climat propice Ă la discussion au sein de programmes d'Ă©ducation sexuelle ciblant les adolescents de sexe masculin afin qu'ils puissent aborder ouvertement le sujet de la sexualitĂ© humaine. Par contre, il est mis en lumiĂšre que le climat du programme APA pouvait facilement dĂ©raper, notamment en raison des thĂšmes de la masculinitĂ© et de l'intimitĂ©, de l'obligation Ă participer au programme, de la gĂȘne Ă parler de sexualitĂ© et d'une mauvaise animation. Pour contrer cette turbulence, la prĂ©sente dĂ©marche Ă©valuative fait valoir la nĂ©cessitĂ© d'outiller et de soutenir les Ă©ducateurs dans leur expĂ©rience d'animation, de miser sur des activitĂ©s dynamiques et ludiques pour susciter l'attention des garçons et de recourir Ă des thĂšmes « masculins », tels que la protection sexuelle et la paternitĂ©. De plus, ce mĂ©moire propose une rĂ©flexion sur l'Ă©valuation de programme en faisant valoir la pertinence de recourir Ă une dĂ©marche Ă©valuative basĂ©e sur un processus nĂ©gociĂ©. Finalement, diffĂ©rentes suggestions sont Ă©noncĂ©es pour bonifier le programme APA.\ud
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MOTS-CLĂS DE LâAUTEUR : Ă©valuation, analyse qualitative, adolescent, Ă©ducation sexuelle, sexualitĂ©, programme d'intervention, formation d'Ă©ducateurs
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