40,691 research outputs found
Flexible modelling in statistics: past, present and future
In times where more and more data become available and where the data exhibit
rather complex structures (significant departure from symmetry, heavy or light
tails), flexible modelling has become an essential task for statisticians as
well as researchers and practitioners from domains such as economics, finance
or environmental sciences. This is reflected by the wealth of existing
proposals for flexible distributions; well-known examples are Azzalini's
skew-normal, Tukey's -and-, mixture and two-piece distributions, to cite
but these. My aim in the present paper is to provide an introduction to this
research field, intended to be useful both for novices and professionals of the
domain. After a description of the research stream itself, I will narrate the
gripping history of flexible modelling, starring emblematic heroes from the
past such as Edgeworth and Pearson, then depict three of the most used flexible
families of distributions, and finally provide an outlook on future flexible
modelling research by posing challenging open questions.Comment: 27 pages, 4 figure
Rectification of a whole-sky photograph as a tool for determining spatial positioning of cumulus clouds
There are no author-identified significant results in this report
Semiconductor manufacturing simulation design and analysis with limited data
This paper discusses simulation design and analysis for Silicon Carbide (SiC) manufacturing operations management at New York Power Electronics Manufacturing Consortium (PEMC) facility. Prior work has addressed the development of manufacturing system simulation as the decision support to solve the strategic equipment portfolio selection problem for the SiC fab design [1]. As we move into the phase of collecting data from the equipment purchased for the PEMC facility, we discuss how to redesign our manufacturing simulations and analyze their outputs to overcome the challenges that naturally arise in the presence of limited fab data. We conclude with insights on how an approach aimed to reflect learning from data can enable our discrete-event stochastic simulation to accurately estimate the performance measures for SiC manufacturing at the PEMC facility
The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude
High resolution (R22,500) spectra for 400 red clump giants, in four
fields within and , were obtained within the GIRAFFE
Inner Bulge Survey (GIBS) project. To this sample we added another 400
stars in Baade's Window, observed with the identical instrumental
configuration. We constructed the metallicity distributions for the entire
sample, as well as for each field individually, in order to investigate the
presence of gradients or field-to-field variations in the shape of the
distributions. The metallicity distributions in the five fields are consistent
with being drawn from a single parent population, indicating the absence of a
gradient along the major axis of the Galactic bar. The global metallicity
distribution is well fitted by two Gaussians. The metal poor component is
rather broad, with a mean at dex and dex.
The metal-rich one is narrower, with mean and
dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with
respect to solar in the metal-poor regime, similar to the one observed for
giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend,
but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is
observed at dex. This \textit{knee} is in agreement with our
previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in
metallicity than the one reported for the Bulge micro lensed dwarf and
sub-giant stars. We found no variation in -element abundance
distributions between different fields.Comment: Accepted for publication in A&
Quenching or Bursting: Star Formation Acceleration--A New Methodology for Tracing Galaxy Evolution
We introduce a new methodology for the direct extraction of galaxy physical
parameters from multi-wavelength photometry and spectroscopy. We use
semi-analytic models that describe galaxy evolution in the context of large
scale cosmological simulation to provide a catalog of galaxies, star formation
histories, and physical parameters. We then apply stellar population synthesis
models and a simple extinction model to calculate the observable broad-band
fluxes and spectral indices for these galaxies. We use a linear regression
analysis to relate physical parameters to observed colors and spectral indices.
The result is a set of coefficients that can be used to translate observed
colors and indices into stellar mass, star formation rate, and many other
parameters, including the instantaneous time derivative of the star formation
rate which we denote the {\it Star Formation Acceleration (SFA)}, We apply the
method to a test sample of galaxies with GALEX photometry and SDSS
spectroscopy, deriving relationships between stellar mass, specific star
formation rate, and star formation acceleration. We find evidence for a
mass-dependent SFA in the green valley, with low mass galaxies showing greater
quenching and higher mass galaxies greater bursting. We also find evidence for
an increase in average quenching in galaxies hosting AGN. A simple scenario in
which lower mass galaxies accrete and become satellite galaxies, having their
star forming gas tidally and/or ram-pressure stripped, while higher mass
galaxies receive this gas and react with new star formation can qualitatively
explain our results.Comment: 33 pages, 31 figures, ApJ accepte
- …