483 research outputs found
The Connection Between Pulsation, Mass Loss and Circumstellar Shells in Classical Cepheids
Recent observations of Cepheids using infrared interferometry and Spitzer
photometry have detected the presence of circumstellar envelopes (CSE) of dust
and it has been hypothesized that the CSE's are due to dust forming in a
Cepheid wind. Here we use a modified Castor, Abbott & Klein formalism to
produce a Cepheid wind, and this is used to estimate the contribution of mass
loss to the Cepheid mass discrepancy Furthermore, we test the OGLE-III
Classical Cepheids using the IR fluxes from the SAGE survey to determine if
Large Magellanic Cloud Cepheids have CSE's. It is found that IR excess is a
common phenomenon for LMC Cepheids and that the resulting mass-loss rates can
explain at least a fraction of the Cepheid mass discrepancy, depending on the
assumed dust-to-gas ratio in the wind.Comment: 5 pages, 3 figures, proceeding for "Stellar Pulsation: Challenges for
Theory and Observation", Santa Fe 200
The additional-mode garden of RR Lyrae stars
Space-based photometric missions revealed a surprising abundance of
millimagnitude-level additional modes in RR Lyrae stars. The modes that appear
in the modulated fundamental-mode (RRab) stars can be ordered into four major
categories. Here we present the distribution of these groups in the Petersen
diagram, and discuss their characteristics and connections to additional modes
observed in other RR Lyrae stars.Comment: 4 pages, 4 figures, proceedings of the Joint
TASC2-KASC9-SPACEINN-HELAS8 Conference "Seismology of the Sun and the Distant
Stars 2016", to be published in EPJ Wo
Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation with Testimator and Schwarz Information Criterion Methods
In this paper, we investigate the linearity versus non-linearity of the Large
Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two
statistical approaches not previously applied to this problem: the testimator
method and the Schwarz Information Criterion (SIC). The testimator method is
extended to multiple stages for the first time, shown to be unbiased and the
variance of the estimated slope can be proved to be smaller than the standard
slope estimated from linear regression theory. The Schwarz Information
Criterion (also known as the Bayesian Information Criterion) is more
conservative than the Akaike Information Criterion and tends to choose lower
order models. By using simulated data sets, we verify that these statistical
techniques can be used to detect intrinsically linear and/or non-linear P-L
relations. These methods are then applied to independent LMC Cepheid data sets
from the OGLE project and the MACHO project, respectively. Our results imply
that there is a change of slope in longer period ranges for all of the data
sets. This strongly supports previous results, obtained from independent
statistical tests, that the observed LMC P-L relation is non-linear with a
break period at/around 10 days.Comment: 9 pages, 5 figures and 3 tables, PASP accepte
Risk attitudes and informal employment in a developing economy
© 2012 Bennett et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License(http://creativecommons.org/licenses/by/2.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.We model an urban labour market in a developing economy, incorporating workers’ risk attitudes. Trade-offs between risk aversion and ability determine worker allocation across formal and informal wage employment, and voluntary and involuntary self employment. Greater risk of informal wage non-payment can raise or lower informal wage employment, depending on the source of risk. Informal wage employment can be reduced by increasing detection efforts or by strengthening contract enforcement for informal wage payment. As the average ability of workers rises, informal wage employment first rises, then falls. Greater demand for formal production may lead to more involuntary self employment
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
The Last Mile in Analyzing Wellbeing and Poverty : Indices of Social Development
__Abstract__
Development practitioners worldwide increasingly recognize the importance of informal institutions - such as norms of cooperation, non-discrimination, or the role of community oversight in the management of investment activities – in affecting well-being, poverty, and even economic growth. There has been little empirical analysis that tests these relationships at the international level. This is largely due to data limitations: few reliable, globally-representative data sources exist that can provide a basis for cross-country comparison of social norms and practice, social trust and community engagement
Taxing the Informal Economy: The Current State of Knowledge and Agendas for Future Research
This paper reviews the literature on taxation of the informal economy, taking stock of key debates
and drawing attention to recent innovations. Conventionally, the debate on whether to tax has frequently focused
on the limited revenue potential, high cost of collection, and potentially adverse impact on small firms. Recent
arguments have increasingly emphasised the more indirect benefits of informal taxation in relation to economic
growth, broader tax compliance, and governance. More research is needed, we argue, into the relevant costs and
benefits for all, including quasi-voluntary compliance, political and administrative incentives for reform, and
citizen-state bargaining over taxation
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