26,618 research outputs found
The Dawes Review 8: Measuring the Stellar Initial Mass Function
The birth of stars and the formation of galaxies are cornerstones of modern
astrophysics. While much is known about how galaxies globally and their stars
individually form and evolve, one fundamental property that affects both
remains elusive. This is problematic because this key property, the birth mass
distribution of stars, referred to as the stellar initial mass function (IMF),
is a key tracer of the physics of star formation that underpins almost all of
the unknowns in galaxy and stellar evolution. It is perhaps the greatest source
of systematic uncertainty in star and galaxy evolution. The past decade has
seen a growing number and variety of methods for measuring or inferring the
shape of the IMF, along with progressively more detailed simulations,
paralleled by refinements in the way the concept of the IMF is applied or
conceptualised on different physical scales. This range of approaches and
evolving definitions of the quantity being measured has in turn led to
conflicting conclusions regarding whether or not the IMF is universal. Here I
review and compare the growing wealth of approaches to our understanding of
this fundamental property that defines so much of astrophysics. I summarise the
observational measurements from stellar analyses, extragalactic studies and
cosmic constraints, and highlight the importance of considering potential IMF
variations, reinforcing the need for measurements to quantify their scope and
uncertainties carefully, in order for this field to progress. I present a new
framework to aid the discussion of the IMF and promote clarity in the further
development of this fundamental field.Comment: Accepted for publication in PASA. 52 pages, 10 figures. A bug in
pasa-mnras.bst causes references beginning with lower-case letters (e.g.,
"de", "van") to be placed at the end of the reference list, rather than
alphabetically. Kindly and skilled people are encouraged to correct this and
share with the PASA editor
Integrated analysis and applications
A select overview is provided of ongoing research focusing on the development and verification of integrated structural analysis and optimal design capabilities for advanced aerospace propulsion and power systems. Subjects discussed include the following: (1) Composites - analytical models (composite mechanics), integrated computational methods, and characterization of composite structural response and durability for resin-, metal-, and ceramic-matrix systems; (2) Advanced inelastic analysis - algorithm/numerical methods for more accurate and efficient analysis; (3) Constitutive modeling - theoretical formulation and characterization of thermoviscoplastic material behavior; (4) Computational simulation - engine structures from components to assembly, and up to an entire engine system subjected to simulated test-stand and mission load histories; (5) Probabilistic structural analysis - quantification of the effects of uncertainty in geometry, material, loads, and boundary conditions on structural response for true reliability assessment; and (6) Interdisciplinary optimization - incorporation of mathematical optimization and multidisciplinary analyses to provide streamlined, autonomous optimal design systems
Matching the Local and Cosmic Star Formation Histories
Given the many recent advances in our understanding of the star formation
history (SFH) of the Local Group and other nearby galaxies, and in the
evolution of star formation with redshift, we present a new comparison of the
comoving space density of the star formation rate as a function of look-back
time for the Local and Distant Universe. We update the Local SFH derived from
the analysis of resolved stellar populations (``fossil records'') in individual
nearby galaxies, based on our own estimations as well as available in the
literature. While the preliminary comparison of SFHs is found to be broadly
consistent, some discrepancies still remain, including an excess of the Local
SFR density in the most recent epoch.Comment: 4 pages, slightly revised version from a contribution to 'Galaxies in
the Local Volume', Sydney, 8 - 13 July 2007, B. Koribalski and H. Jerjen, ed
The Phoenix survey: the pairing fraction of faint radio sources
The significance of tidal interactions in the evolution of the faint radio
population (sub-mJy) is studied using a deep and homogeneous radio survey (1.4
GHz), covering an area of 3.14 deg and complete to a flux density of 0.4
mJy. Optical photometric and spectroscopic data are also available for this
sample. A statistical approach is employed to identify candidate physical
associations between radio sources and optically selected `field' galaxies. We
find an excess of close pairs around optically identified faint radio sources,
albeit at a low significance level, implying that the pairing fraction of the
sub-mJy radio sources is similar to that of `field' galaxies (at the same
magnitude limit) but higher than that of local galaxies.Comment: 5 pages, 4 figures. Accepted for publication in MNRAS Letter
TQM and CSR nexus
Purpose:
The aim of this paper is to explore the similarities and differences between Total Quality Management (TQM) and Corporate Social Responsibility (CSR). Moreover, the paper considers the implications of these similarities and differences for the future development of TQM and CSR.
Methodological approach:
Structured discourse analysis is used to systematically explore these two discursive subjects. Both concepts encompass discursive ideas and practices.
Findings:
Our analyses suggest that the two concepts share similar philosophical roots, that there is a substantial overlap between the elements of the two concepts, and that the ultimate expected outcomes shows significant similarities. Despite these similarities however, implementation of TQM will not necessarily result in CSR.
Practical implications:
Our findings lead to the conclusion that it is important to recognise the specific needs of CSR and include them as an implicit part of TQM. This conclusion has an important practical and descriptive theoretical implication and the extent to which CSR is diffused as a part of TQM depends on it.
Research implications:
Our analysis highlights the need for the development of a descriptive theory, that is to say, the identification of the mechanism(s) through which elements of CSR could be developed and implemented alongside that of TQM.
Original/value:
The question of the intersection between CSR and TQM has attracted the interest of other researchers. The majority of the previous work is normative. We contribute to this developing literature by adopting a systematic discursive approach using philosophy, elements of TQM / CSR process and outcomes as the framework for the analysis
The radio spectra of reddened 2MASS QSOs: evidence for young radio jets
Multifrequency radio continuum observations (1.4-22 GHz) of a sample of
reddened QSOs are presented. We find a high incidence (13/16) of radio spectral
properties, such as low frequency turnovers, high frequency spectral breaks or
steep power-law slopes, similar to those observed in powerful compact steep
spectrum (CSS) and gigahertz-peaked spectrum (GPS) sources. The radio data are
consistent with relatively young radio jets with synchotron ages <1e6-1e7yr.
This calculation is limited by the lack of high resolution (milli-arcsec) radio
observations. For the one source in the sample that such data are available a
much younger radio age is determined, <2e3yr, similar to those of GPS/CSS
sources. These findings are consistent with claims that reddened QSOs are young
systems captured at the first stages of the growth of their supermassive black
holes. It also suggests that expanding radio lobes may be an important feedback
mode at the early stages of the evolution of AGN.Comment: 9 pages, to appear in MNRA
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