246 research outputs found
SPLINE FUNCTIONS: THEIR USE IN ESTIMATING NON-REVERSIBLE RESPONSE
The Objectives of this paper are: (1) to introduce the concept of spline functions; and (2) to account for complete and partial non-reversibility with spline functions. This paper illustrates this approach using a supply response example.Research Methods/ Statistical Methods,
Aligning modes of organization with technology: Critical transactions in the reform of infrastructures
This paper is about the alignment of technology and modes of organization in infrastructures in the context of their reform. Since infrastructures are characterized by strong technical complementarities, we explore the resulting 'critical technical functions' that need to be performed in order to guarantee the expected technical performance of the system. We characterize 'critical transactions' as essential to provide adequate support to these functions. We distinguish various modes of organization that can effectively coordinate these critical transactions. We argue that the features of these transactions determine the alignment between organization and technology and should be taken explicitly into account when reforming infrastructures.Transaction costs; technology; institutional change; reforms of infrastructures
Understanding the development of temporary agency work in Europe
This article develops an explanatory framework for understanding the growth and development of temporary agency work (TAW) and the related industry. The analysis shows that explanations based on economic logic are helpful in understanding the choice of TAW in general. These explanations, however, fall short when trying to explain the growth of agency work over time or the variation in its use among European countries. To cope with these shortcomings, we extend our explanatory base to include a variety of sociocultural dynamics. Our analysis shows how deep-seated national work-related values ('deep embeddedness') affect the way TAW is regulated nationally. It also demonstrates how differences in more changeable norms, attitudes and practices ('dynamic embeddedness') affect the process of embedding agency work as a societally acceptable phenomenon, providing a basis for its subsequent proliferation
Carbon-Rich Mira Variables: Radial Velocities and Distances
Optical radial velocities have been measured for 38 C-type Mira variables.
These data together with others in the literature are used to study the
differences between optical and CO mm observations for C-Miras and the
necessary corrections to the optical velocities are derived in order to obtain
the true radial velocities of the variables. The difference between absorption
and emission line velocities is also examined. A particularly large difference
(+30 km\s) is found in the case of the H-alpha emission line. A catalogue is
given of 177 C-Miras with estimated distances and radial velocities. The
distances are based on bolometric magnitudes derived in Paper I using SAAO
observations or (for 60 of the stars) using non-SAAO photometry. In the latter
case the necessary transformations to the SAAO system are derived. These data
will be used in paper III to study the kinematics of the C-Miras.Comment: 11 pages, accepted for publication in MNRA
The distribution of H13CN in the circumstellar envelope around IRC+10216
H13CN J=8-7 sub-millimetre line emission produced in the circumstellar
envelope around the extreme carbon star IRC+10216 has been imaged at
sub-arcsecond angular resolution using the SMA. Supplemented by a detailed
excitation analysis the average fractional abundance of H13CN in the inner wind
(< 5E15 cm) is estimated to be about 4E-7, translating into a total HCN
fractional abundance of 2E-5 using the isotopic ratio 12C/13C=50.
Multi-transitional single-dish observations further requires the H13CN
fractional abundance to remain more or less constant in the envelope out to a
radius of about 4E16 cm, where the HCN molecules are effectively destroyed,
most probably, by photodissociation. The large amount of HCN present in the
inner wind provides effective line cooling that can dominate over that
generated from CO line emission. It is also shown that great care needs to be
taken in the radiative transfer modelling where non-local, and non-LTE, effects
are important and where the radiation field from thermal dust grains plays a
major role in exciting the HCN molecules. The amount of HCN present in the
circumstellar envelope around IRC+10216 is consistent with predicted
photospheric values based on equilibrium chemical models and indicates that any
non-equilibrium chemistry occurring in the extended pulsating atmosphere has no
drastic net effect on the fractional abundance of HCN molecules that enters the
outer envelope. It further suggests that few HCN molecules are incorporated
into dust grains.Comment: Accepted for publication in ApJ. 20 pages, 7 figure
Period-Luminosity Relations Derived from the OGLE-III Fundamental Mode Cepheids
In this Paper, we have derived Cepheid period-luminosity (P-L) relations for
the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on the data
released from OGLE-III. We have applied an extinction map to correct for the
extinction of these Cepheids. In addition to the VIW band P-L relations, we
also include JHK and four Spitzer IRAC band P-L relations, derived by matching
the OGLE-III Cepheids to the 2MASS and SAGE datasets, respectively. We also
test the non-linearity of the Cepheid P-L relations based on
extinction-corrected data. Our results (again) show that the LMC P-L relations
are non-linear in VIJH bands and linear in KW and the four IRAC bands,
respectively.Comment: 6 pages, 3 figures and 3 tables, ApJ accepte
Stellar Models and Yields of Asymptotic Giant Branch Stars
We present stellar yields calculated from detailed models of low and
intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a
range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th
of the solar metallicity. Each model was evolved from the zero age main
sequence to near the end of the thermally-pulsing AGB phase, and through all
intermediate phases including the core He-flash for stars initially less
massive than 2.5Msun. For each mass and metallicity, we provide tables
containing structural details of the stellar models during the TP-AGB phase,
and tables of the stellar yields for 74 species from hydrogen through to
sulphur, and for a small number of iron-group nuclei. All tables are available
for download. Our results have many applications including use in population
synthesis studies and the chemical evolution of galaxies and stellar systems,
and for comparison to the composition of AGB and post-AGB stars and planetary
nebulae.Comment: 26 pages; to appear in Publications of the Astronomical Society of
Australia (PASA); typos fixed in the text and in Tables 4 and
Carbon-Rich Mira Variables: Kinematics and Absolute Magnitudes
The kinematics of galactic C-Miras are discussed on the basis of the
bolometric magnitudes and radial velocities of Papers I and II of this series.
Differential galactic rotation is used to derive a zero-point for the
bolometric period-luminosity relation which is in satisfactory agreement with
that inferred from the LMC C-Miras. We find for the galactic Miras, Mbol =
-2.54logP + 2.06 (+/- 0.24), where the slope is taken from the LMC. The mean
velocity dispersion, together with the data of Nordstroem et al. and the Padova
models, leads to a mean age for our sample of C-Miras of 1.8 +/- 0.4 Gyr and a
mean initial mass of 1.8 +/-0.2 solar masses. Evidence for a variation of
velocity dispersion with period is found, indicating a dependence of period on
age and initial mass, the longer period stars being younger. We discuss the
relation between the O- and C-Miras and also their relative numbers in
different systems.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Testing Mass Loss in Large Magellanic Cloud Cepheids using Infrared and Optical Observations II. Predictions and Tests of the OGLE-III Fundamental-Mode Cepheids
In this article, we test the hypothesis that Cepheids have infrared excesses
due to mass loss. We fit a model using the mass-loss rate and the stellar
radius as free parameters to optical observations from the OGLE-III survey and
infrared observations from the 2MASS and SAGE data sets. The sample of Cepheids
have predicted minimum mass-loss rates ranging from zero to
, where the rates depend on the chosen dust properties. We use the
predicted radii to compute the Period-Radius relation for LMC Cepheids, and to
estimate the uncertainty caused by the presence of infrared excess for
determining angular diameters with the infrared surface brightness technique.
Finally, we calculate the linear and non-linear Period-Luminosity (P-L)
relations for the LMC Cepheids at VIJHK + IRAC wavelengths and we find that the
P-L relations are consistent with being non-linear at infrared wavelengths,
contrary to previous results.Comment: 17 pages, 12 figures, 5 tables, ApJ Accepte
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