794 research outputs found
The escape fraction of ionizing photons during the Epoch of Reionization:Observability with the Square Kilometre Array
One of the most important parameters in characterizing the Epoch of Reionization, the escape fraction of ionizing photons, fesc, remains unconstrained both observationally and theoretically. With recent work highlighting the impact of galaxy-scale feedback on the instantaneous value of fesc, it is important to develop a model in which reionization is self-consistently coupled to galaxy evolution. In this work, we present such a model and explore how physically motivated functional forms of fesc affect the evolution of ionized hydrogen within the intergalactic medium. Using the 21 cm power spectrum evolution, we investigate the likelihood of observationally distinguishing between a constant fesc and other models that depend upon different forms of galaxy feedback. We find that changing the underlying connection between fesc and galaxy feedback drastically alters the large-scale 21 cm power. The upcoming Square Kilometre Array Low Frequency instrument possesses the sensitivity to differentiate between our models at a fixed optical depth, requiring only 200 h of integration time focused on redshifts z = 7.5-8.5. Generalizing these results to account for a varying optical depth will require multiple 800 h observations spanning redshifts z = 7-10. This presents an exciting opportunity to observationally constrain one of the most elusive parameters during the Epoch of Reionization
A Corpus Based Analysis of Noun Modification in Empirical Research Articles in Applied Linguistics
Previous research has established the importance of the nouns and noun modification in academic writing because of their commonness and complexity. However, little is known about how noun modification varies across the rhetorical sections of research articles. Such a perspective is important because it reflects the interplay between communicative function and linguistic form.
This study used a corpus of empirical research articles from the fields of applied linguistics and language teaching to explore the connection between article sections (Introduction, Methods, Results, Discussion; IMRD) and six types of noun modification: relative clauses, ing-clause postmodifiers, ed-clause postmodifiers, prepositional postmodifiers, premodifying nouns, and attributive adjectives. First the frequency of these six types of noun modification was compared across IMRD sections. Second, the study also used a hand coded analysis of the structure and structural patterns of a sample of noun phrases through IMRD sections.
The results of the analyses showed that noun modification is not uniform across IMRD sections. Significant differences were found in the rates of use for attributive adjectives, premodifying nouns, and prepositional phrase postmodifiers. There were no significant differences between sections for relative clauses, ing-clause postmodifiers, or ed-clause postmodifiers. The differences between sections for attributive adjectives, premodifying nouns, and prepositional phrases illustrate the way the functions of these structures intersects with the functions of IMRD sections. For example, Methods sections describe research methods, which often have premodifying nouns (corpus analysis, conversation analysis, speech sample, etc.); this function of Methods sections results in a higher use of premodifying nouns compared to other sections. Results for structures of noun phrase across IMRD sections showed that the common noun modification patterns, such as premodifying noun only or attributive adjective with prepositional phrase postmodifier, were mostly consistent across sections. Noun phrase structures including pre-/post- or no modification did have differences across sections, with Introduction sections the most frequently modified and Methods sections the least frequently modified. The different functions of IMRD sections call for different rates of usage for noun modification, and the results reflected this.
The results of this research benefit teachers of graduate students of applied linguistics in students\u27 research reading and writing by describing the use of noun modification in the sections of empirical research articles and aiding teachers in the design of materials to clarify the use of noun modification in these IMRD sections
Escalades dans les Alpes 1860-1869 d’Edward Whymper, une oeuvre à la croisée de l’art et de la science
Mémoire du Master 1 Cultures de l\u27écrit et de l\u27image portant sur le récit d’Edward Whymper, "Escalades dans les Alpes 1860-1869"
Astraeus - III. The environment and physical properties of reionization sources
In this work, we use the {\sc astraeus} (seminumerical rAdiative tranSfer
coupling of galaxy formaTion and Reionization in N-body dArk mattEr
simUlationS) framework which couples galaxy formation and reionization in the
first billion years. Exploring a number of models for reionization feedback and
the escape fraction of ionizing radiation from the galactic environment
(), we quantify how the contribution of star-forming galaxies
{(with halo masses M)} to reionization depends on the
radiative feedback model, , and the environmental over-density.
Our key findings are: (i) for constant models,
intermediate-mass galaxies (with halo masses of M
and absolute UV magnitudes of to ) in
intermediate-density regions drive reionization; (ii) scenarios where
increases with decreasing halo mass shift the galaxy
population driving reionization to lower-mass galaxies
(M) with lower luminosities ()
and over-densities; (iii) reionization imprints its topology on the ionizing
emissivity of low-mass galaxies (M) through
radiative feedback. Low-mass galaxies experience a stronger suppression of star
formation by radiative feedback and show lower ionizing emissivities in
over-dense regions; (iv) a change in with galaxy properties
has the largest impact on the sources of reionization and their detectability,
with the radiative feedback strength and environmental over-density playing a
sub-dominant role; (v) JWST-surveys (with a limiting magnitude of ) will be able to detect the galaxies providing () of reionization photons at for constant models
(scenarios where increases with decreasing halo mass).Comment: 14 pages, 13 figures, accepted for publication in MNRA
Escalades dans les Alpes 1860-1869 d’Edward Whymper, une oeuvre à la croisée de l’art et de la science - Annexes
Annexes du mémoire du Master 1 Cultures de l\u27écrit et de l\u27image portant sur le récit d’Edward Whymper, "Escalades dans les Alpes 1860-1869"
Documentaires de Jean-Paul Janssen, esthétique et médiatisation de l’escalade de Patrick Edlinger (Les)
Mémoire du Master 2 Cultures de l\u27écrit et de l\u27image portant sur documentaires de Jean-Paul Janssen, esthétique et médiatisation de l’escalade de Patrick Edlinger
Astraeus VIII: A new framework for Lyman- emitters applied to different reionisation scenarios
We use the {\sc astraeus} framework to investigate how the visibility and
spatial distribution of Lyman- (Ly) emitters (LAEs) during
reionisation is sensitive to a halo mass-dependent fraction of ionising
radiation escaping from the galactic environment () and the
ionisation topology. To this end, we consider the two physically plausible
bracketing scenarios of increasing and decreasing with rising
halo mass. We derive the corresponding observed Ly luminosities of
galaxies for three different analytic Ly line profiles and associated
Ly escape fraction () models:
importantly, we introduce two novel analytic Ly line profile models
that describe the surrounding interstellar medium (ISM) as dusty gas clumps.
They are based on parameterising results from radiative transfer simulations,
with one of them relating to
by assuming the ISM of being interspersed with low-density
tunnels. Our key findings are: (i) for dusty gas clumps, the Ly line
profile develops from a central to double peak profile as a galaxy's halo mass
increases; (ii) LAEs are galaxies with located in
overdense and highly ionised regions; (iii) for this reason, the spatial
distribution of LAEs is primarily sensitive to the global ionisation fraction
and only weakly in second-order to the ionisation topology or a halo
mass-dependent ; (iv) furthermore, as the observed Ly
luminosity functions reflect the Ly emission from more massive
galaxies, there is a degeneracy between the -dependent
intrinsic Ly luminosity and the Ly attenuation by dust in the
ISM if does not exceed .Comment: 25 pages, 9 figures; accepted for publication in MNRA
Astraeus VII: The environmental-dependent assembly of galaxies in the Epoch of Reionization
Using the ASTRAEUS (semi-numerical rAdiative tranSfer coupling of galaxy
formaTion and Reionization in N-body dark matter simUlationS) framework, we
explore the impact of environmental density and radiative feedback on the
assembly of galaxies and their host halos during the Epoch of Reionization. The
ASTRAEUS framework allows us to study the evolution of galaxies with masses
() in wide variety of
environment ( averaged over ). We find that : (i) there exists a mass- and redshift- dependent
"characteristic" environment (, up to ) at which
galaxies are most efficient at accreting dark matter, e.g at a rate of
of their mass every Myr at ; (ii) the number of minor and major mergers
and their contributions to the dark matter assembly increases with halo mass at
all redshifts and is mostly independent of the environment; (iii) at
minor mergers contribute slightly more (by up to ) to the dark
matter assembly while for the stellar assembly, major mergers dominate the
contribution from minor mergers for
galaxies; (iv) radiative feedback quenches star formation more in low-mass
galaxies () in over-dense environments
(); dominated by their major branch, this yields
star formation histories biased towards older ages with a slower redshift
evolution.Comment: 17 pages, 15 figures, submitted to MNRAS, comments welcome
- …