4,382 research outputs found
Fitting Isochrones to Open Cluster photometric data: A new global optimization tool
We present a new technique to fit color-magnitude diagrams of open clusters
based on the Cross-Entropy global optimization algorithm. The method uses
theoretical isochrones available in the literature and maximizes a weighted
likelihood function based on distances measured in the color-magnitude space.
The weights are obtained through a non parametric technique that takes into
account the star distance to the observed center of the cluster, observed
magnitude uncertainties, the stellar density profile of the cluster among
others. The parameters determined simultaneously are distance, reddening, age
and metallicity. The method takes binary fraction into account and uses a
Monte-Carlo approach to obtain uncertainties on the determined parameters for
the cluster by running the fitting algorithm many times with a re-sampled data
set through a bootstrapping procedure. We present results for 9 well studied
open clusters, based on 15 distinct data sets, and show that the results are
consistent with previous studies. The method is shown to be reliable and free
of the subjectivity of most previous visual isochrone fitting techniques.Comment: 19 pages, 25 figures, accepted for publication in
Astronomy&Astrophysic
Interpolation of nonstationary high frequency spatial-temporal temperature data
The Atmospheric Radiation Measurement program is a U.S. Department of Energy
project that collects meteorological observations at several locations around
the world in order to study how weather processes affect global climate change.
As one of its initiatives, it operates a set of fixed but irregularly-spaced
monitoring facilities in the Southern Great Plains region of the U.S. We
describe methods for interpolating temperature records from these fixed
facilities to locations at which no observations were made, which can be useful
when values are required on a spatial grid. We interpolate by conditionally
simulating from a fitted nonstationary Gaussian process model that accounts for
the time-varying statistical characteristics of the temperatures, as well as
the dependence on solar radiation. The model is fit by maximizing an
approximate likelihood, and the conditional simulations result in
well-calibrated confidence intervals for the predicted temperatures. We also
describe methods for handling spatial-temporal jumps in the data to interpolate
a slow-moving cold front.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS633 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Tracking moving optima using Kalman-based predictions
The dynamic optimization problem concerns finding an optimum in a changing environment. In the field of evolutionary algorithms, this implies dealing with a timechanging fitness landscape. In this paper we compare different techniques for integrating motion information into an evolutionary algorithm, in the case it has to follow a time-changing optimum, under the assumption that the changes follow a nonrandom law. Such a law can be estimated in order to improve the optimum tracking capabilities of the algorithm. In particular, we will focus on first order dynamical laws to track moving objects. A vision-based tracking robotic application is used as testbed for experimental comparison
Comparison of Gaussian process modeling software
Gaussian process fitting, or kriging, is often used to create a model from a
set of data. Many available software packages do this, but we show that very
different results can be obtained from different packages even when using the
same data and model. We describe the parameterization, features, and
optimization used by eight different fitting packages that run on four
different platforms. We then compare these eight packages using various data
functions and data sets, revealing that there are stark differences between the
packages. In addition to comparing the prediction accuracy, the predictive
variance--which is important for evaluating precision of predictions and is
often used in stopping criteria--is also evaluated
A Prediction Modeling Framework For Noisy Welding Quality Data
Numerous and various research projects have been conducted to utilize historical manufacturing process data in product design. These manufacturing process data often contain data inconsistencies, and it causes challenges in extracting useful information from the data. In resistance spot welding (RSW), data inconsistency is a well-known issue. In general, such inconsistent data are treated as noise data and removed from the original dataset before conducting analyses or constructing prediction models. This may not be desirable for every design and manufacturing applications since every data can contain important information to further explain the process. In this research, we propose a prediction modeling framework, which employs bootstrap aggregating (bagging) with support vector regression (SVR) as the base learning algorithm to improve the prediction accuracy on such noisy data. Optimal hyper-parameters for SVR are selected by particle swarm optimization (PSO) with meta-modeling. Constructing bagging models require
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more computational costs than a single model. Also, evolutionary computation algorithms, such as PSO, generally require a large number of candidate solution evaluations to achieve quality solutions. These two requirements greatly increase the overall computational cost in constructing effective bagging SVR models. Meta-modeling can be employed to reduce the computational cost when the fitness or constraints functions are associated with computationally expensive tasks or analyses. In our case, the objective function is associated with constructing bagging SVR models with candidate sets of hyper-parameters. Therefore, in regards to PSO, a large number of bagging SVR models have to be constructed and evaluated, which is computationally expensive. The meta-modeling approach, called MUGPSO, developed in this research assists PSO in evaluating these candidate solutions (i.e., sets of hyper-parameters). MUGPSO approximates the fitness function of candidate solutions. Through this method, the numbers of real fitness function evaluations (i.e., constructing bagging SVR models) are reduced, which also reduces the overall computational costs. Using the Meta2 framework, one can expect an improvement in the prediction accuracy with reduced computational time. Experiments are conducted on three artificially generated noisy datasets and a real RSW quality dataset. The results indicate that Meta2 is capable of providing promising solutions with noticeably reduced computational costs
Proportional Topology Optimization: A new non-gradient method for solving stress constrained and minimum compliance problems and its implementation in MATLAB
A new topology optimization method called the Proportional Topology
Optimization (PTO) is presented. As a non-gradient method, PTO is simple to
understand, easy to implement, and is also efficient and accurate at the same
time. It is implemented into two MATLAB programs to solve the stress
constrained and minimum compliance problems. Descriptions of the algorithm and
computer programs are provided in detail. The method is applied to solve three
numerical examples for both types of problems. The method shows comparable
efficiency and accuracy with an existing gradient optimality criteria method.
Also, the PTO stress constrained algorithm and minimum compliance algorithm are
compared by feeding output from one algorithm to the other in an alternative
manner, where the former yields lower maximum stress and volume fraction but
higher compliance compared to the latter. Advantages and disadvantages of the
proposed method and future works are discussed. The computer programs are
self-contained and publicly shared in the website www.ptomethod.org.Comment: 18 pages, 8 figures, and 2 appendices (MATLAB codes
Solar-like oscillations in the G9.5 subgiant beta Aquilae
An interesting asteroseismic target is the G9.5 IV solar-like star beta Aql.
This is an ideal target for asteroseismic investigations, because precise
astrometric measurements are available from Hipparcos that greatly help in
constraining the theoretical interpretation of the results. The star was
observed during six nights in August 2009 by means of the high-resolution
\'echelle spectrograph SARG operating with the TNG 3.58 m Italian telescope on
the Canary Islands, exploiting the iodine cell technique. We present the result
and the detailed analysis of high-precision radial velocity measurements, where
the possibility of detecting time individual p-mode frequencies for the first
and deriving their corresponding asymptotic values will be discussed. The
time-series analysis carried out from \sim 800 collected spectra shows the
typical p-mode frequency pattern with a maximum centered at 416 \muHz. In the
frequency range 300 - 600 \muHz we identified for the first time six high S/N
(\gtrsim 3.5) modes with l = 0,2 and 11 < n < 16 and three possible candidates
for mixed modes (l = 1), although the p-mode identification for this type of
star appears to be quite difficult owing to a substantial presence of avoided
crossings. The large frequency separation and the surface term from the set of
identified modes by means of the asymptotic relation were derived for the first
time. Their values are \Delta \nu = 29.56 \pm 0.10 \muHz and \epsilon = 1.29
\pm 0.04, consistent with expectations. The most likely value for the small
separation is \delta\nu_{02} = 2.55 \pm 0.71 \muHz.Comment: 8 pages, 8 figures, 3 tables, accepted by A&
ACOUSTIC DESIGN OPTIMIZATION WITH ISOGEOMETRIC ANALYSIS AND DIFFERENTIAL EVOLUTION
The objective of this study is to utilize shape optimization to enhance the performance of devices relying on acoustic wave propagation. Particularly, the shape of a horn speaker and an acoustic energy harvester were optimized to enhance their performance at targeted frequencies. High order Isogeometric Analysis (IGA) was performed to estimate the acoustic pressure with minimum geometry and pollution errors [1]. The analysis platform was then combined with Differential Evolution (DE) to optimize the geometry of the horn speaker and energy harvester at a given frequency. These cases effectively demonstrate two applications of Isogeomtric shape optimization for devices relying on acoustic wave propagation. The horn shape was previously optimized using conventional FEA [2]. The study performed to optimize the sound energy harvester demonstrates the effectiveness of isogeometric shape optimization for novel applications. It was shown that the proposed platform can generate tunable designs that reach their optimum performance at the desired frequencies. The back-reflection of the horn speaker was reduced considerably by optimizing the shape of the horn boundary. Tikhonov regularization was used to avoid finding wiggly solutions and ensure ease of manufacturing. The geometry of the energy harvester was optimized and tuned for a range of targeted frequencies by optimizing its defining parameters, its placement angle, and developing an optimized variable channel width. The DE algorithm, which is known for finding the global minimum, successfully updated the design geometries and identified the global minimum in most cases studied in this thesis
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