83,487 research outputs found
Isochrone fitting in the Gaia era
Context. Currently galactic exploration is being revolutionized by a flow of
new data: Gaia provides measurements of stellar distances and kinematics;
growing numbers of spectroscopic surveys provide values of stellar atmospheric
parameters and abundances of elements; and Kepler and K2 missions provide
asteroseismic information for an increasing number of stars. Aims. In this work
we aim to determine stellar distances and ages using Gaia and
spectrophotometric data in a consistent way. We estimate precisions of age and
distance determinations with Gaia end-of-mission and TGAS parallax precisions.
Methods. To this end we incorporated parallax and extinction data into the
isochrone fitting method used in the Unified tool to estimate Distances, Ages,
and Masses (UniDAM). We prepared datasets that allowed us to study the
improvement of distance and age estimates with the inclusion of TGAS and Gaia
end-of-mission parallax precisions in isochrone fitting. Results. Using TGAS
parallaxes in isochrone fitting we are able to reduce distance and age estimate
uncertainties for TGAS stars for distances up to 1 kpc by more than one third,
compared to results based only on spectrophotometric data. With Gaia
end-of-mission parallaxes in isochrone fitting we will be able to further
decrease our distance uncertainties by about a factor of 20 and age
uncertainties by a factor of two for stars up to 10 kpc away from the Sun.
Conclusions. We demonstrate that we will be able to improve our distance
estimates for about one third of stars in spectroscopic surveys and to decrease
log(age) uncertainties by about a factor of two for over 80% of stars as
compared to the uncertainties obtained without parallax priors using Gaia
end-of-mission parallaxes consistently with spectrophotometry in isochrone
fitting .Comment: 15 pages, 3 figures, 4 table
For principled model fitting in mathematical biology
The mathematical models used to capture features of complex, biological
systems are typically non-linear, meaning that there are no generally valid
simple relationships between their outputs and the data that might be used to
validate them. This invalidates the assumptions behind standard statistical
methods such as linear regression, and often the methods used to parameterise
biological models from data are ad hoc. In this perspective, I will argue for
an approach to model fitting in mathematical biology that incorporates modern
statistical methodology without losing the insights gained through non-linear
dynamic models, and will call such an approach principled model fitting.
Principled model fitting therefore involves defining likelihoods of observing
real data on the basis of models that capture key biological mechanisms.Comment: 7 pages, 3 figures. To appear in Journal of Mathematical Biology. The
final publication is available at Springer via
http://dx.doi.org/10.1007/s00285-014-0787-
Track fitting in slightly inhomogeneous magnetic fields
A fitting method to reconstruct the momentum and direction of charged
particles in slightly inhomogeneous magnetic fields is presented in detail. For
magnetic fields of the order of 1 T and inhomogeneity gradients as large as 1
T/m the typical momentum bias due to the proposed approximations is of the
order of few MeV, to be compared with scattering components of the order of 20
MeV or even larger. This method is currently being employed in the
reconstruction programs of the AMS experiment.Comment: 12 pages, Nulc. Instr. Meth. A accepte
Performance test of QU-fitting in cosmic magnetism study
QU-fitting is a standard model-fitting method to reconstruct distribution of
magnetic fields and polarized intensity along a line of sight (LOS) from an
observed polarization spectrum. In this paper, we examine the performance of
QU-fitting by simulating observations of two polarized sources located along
the same LOS, varying the widths of the sources and the gap between them in
Faraday depth space, systematically. Markov Chain Monte Carlo (MCMC) approach
is used to obtain the best-fit parameters for a fitting model, and Akaike and
Bayesian Information Criteria (AIC and BIC, respectively) are adopted to select
the best model from four fitting models. We find that the combination of MCMC
and AIC/BIC works fairly well in model selection and estimation of model
parameters in the cases where two sources have relatively small widths and a
larger gap in Faraday depth space. On the other hand, when two sources have
large width in Faraday depth space, MCMC chain tends to be trapped in a local
maximum so that AIC/BIC cannot select a correct model. We discuss the causes
and the tendency of the failure of QU-fitting and suggest a way to improve it.Comment: 8 pages, 9 figures, submitted to MNRA
A Novel Generic Framework for Track Fitting in Complex Detector Systems
This paper presents a novel framework for track fitting which is usable in a
wide range of experiments, independent of the specific event topology, detector
setup, or magnetic field arrangement. This goal is achieved through a
completely modular design. Fitting algorithms are implemented as
interchangeable modules. At present, the framework contains a validated Kalman
filter. Track parameterizations and the routines required to extrapolate the
track parameters and their covariance matrices through the experiment are also
implemented as interchangeable modules. Different track parameterizations and
extrapolation routines can be used simultaneously for fitting of the same
physical track. Representations of detector hits are the third modular
ingredient to the framework. The hit dimensionality and orientation of planar
tracking detectors are not restricted. Tracking information from detectors
which do not measure the passage of particles in a fixed physical detector
plane, e.g. drift chambers or TPCs, is used without any simplifications. The
concept is implemented in a light-weight C++ library called GENFIT, which is
available as free software
retro fitting in
Consumer culture has become a driving force within western society through the rise of expendable goods and the lower costs of manufacturing. The good life has now been made available to a much greater portion of society and as a result, possessions as signifiers of status have lost much of their exclusivity, but none of its effectiveness. How does one assert individuality by the products they choose?
A primary driving force of consumer culture is that goods have a designated obsolescence that is perhaps only surpassed by the users desire for something new sooner. This rapid rate of replacement is paralleled in the rapidity of Singapore\u27s deployment of housing developments for its equally rapid growing population. A primary issue that has grown out of this explosion of government constructed housing is the role of the individual and how much control the individual can assert over their own space.
By adopting the tenets of consumer culture: the short lifespan of products,the aspiration to obtain better things and the cultivation of consumer choice, the existing consumer conditions can be harnessed to benefit the public housing inhabitant. By challenging the distinction between what is a consumer good and what is a consumer architecture the consumer/inhabitant can affect their space just as easily as they are able to change the perception of their identity through consumer choices of designed goods
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