264 research outputs found
Period Analysis using the Least Absolute Shrinkage and Selection Operator (Lasso)
We introduced least absolute shrinkage and selection operator (lasso) in
obtaining periodic signals in unevenly spaced time-series data. A very simple
formulation with a combination of a large set of sine and cosine functions has
been shown to yield a very robust estimate, and the peaks in the resultant
power spectra were very sharp. We studied the response of lasso to low
signal-to-noise data, asymmetric signals and very closely separated multiple
signals. When the length of the observation is sufficiently long, all of them
were not serious obstacles to lasso. We analyzed the 100-year visual
observations of delta Cep, and obtained a very accurate period of 5.366326(16)
d. The error in period estimation was several times smaller than in Phase
Dispersion Minimization. We also modeled the historical data of R Sct, and
obtained a reasonable fit to the data. The model, however, lost its predictive
ability after the end of the interval used for modeling, which is probably a
result of chaotic nature of the pulsations of this star. We also provide a
sample R code for making this analysis.Comment: 9 pages, 13 figures, accepted for publication in PAS
Starspots on the fastest rotators in the Beta Pic moving group
Aims: We carried out high-resolution spectroscopy and BV(I)_C photometric
monitoring of the two fastest late-type rotators in the nearby Beta Pictoris
moving group, HD199143 (F7V) and CD-641208 (K7V). The motivation for this work
is to investigate the rotation periods and photospheric spot patterns of these
very young stars, with a longer term view to probing the evolution of rotation
and magnetic activity during the early phases of main-sequence evolution. We
also aim to derive information on key physical parameters, such as rotational
velocity and rotation period. Methods: We applied maximum entropy (ME) and
Tikhonov regularizing (TR) criteria to derive the surface spot map
distributions of the optical modulation observed in HD199143 (F7 V) and
CD-641208 (K7V). We also used cross-correlation techniques to determine stellar
parameters such as radial velocities and rotational velocities. Lomb-Scargle
periodograms were used to obtain the rotational periods from differential
magnitude time series. Results: We find periods and inclinations of 0.356 days
and 21.5deg for HD199143, and 0.355 days and 50.1deg for CD-641208. The spot
maps of HD199143 obtained from the ME and TR methods are very similar, although
the latter gives a smoother distribution of the filling factor. Maps obtained
at two different epochs three weeks apart show a remarkable increase in spot
coverage amounting to ~7% of the surface of the photosphere over a time period
of only ~20 days. The spot maps of CD-641208 from the two methods show good
longitudinal agreement, whereas the latitude range of the spots is extended to
cover the whole visible hemisphere in the TR map. The distributions obtained
from the first light curve of HD199143 show the presence of an extended and
asymmetric active longitude with the maximum filling factor at longitude
~325degree.Comment: Accepted by A&A. 13 pages, 13 figures (4 online included), 5 Table
Harmonic analysis of power system signals using a new regularized adaptive windowed lomb periodogram
This paper proposes a new regularized adaptive windowed Lomb periodogram (RAWLP) method for time-frequency analysis of non-stationary power signals. It extends the conventional Lomb periodogram by estimating the periodogram locally using the weighted least-squares (WLS) estimator. Instead of employing one constant window in WLS, variable window bandwidth is adaptively selected by the intersection of confidence intervals (ICI) method to achieve a better tradeoff between time resolution and frequency resolution. Furthermore, regularization techniques are incorporated in the AWLP to further improve its performance by reducing the variance of the estimator. Simulation results show that the proposed RAWLP method has superior performance over windowed Lomb periodogram with one constant bandwidth for estimating the harmonic and interharmonic frequencies in power systems. © 2010 IEEE.published_or_final_versionThe 1st International Conference on Green Circuits and Systems (ICGCS 2010), Shanghai, China, 21-23 June 2010. In Proceedings of the 1st ICGCS, 2010, p. 567-57
Period Estimation and Denoising Families of Nonuniformly Sampled Time Series
Nonuniformly sampled time series are common in astronomy, finance, and other areas of research. Commonly, these time series belong to a family of signals recorded from the same phenomenon. Period estimation and denoising of such data relies on periodograms. In particular, the Lomb-Scargle periodogram and its extension, the Multiband Lomb-Scargle, are at the forefront of time series period estimation. However, these methods are not without laws. This paper explores alternatives to the Lomb-Scargle and Multiband Lomb-Scargle. In particular, this thesis uses regularized least squares and the convolution theorem to introduce a spectral consensus model of a family of nonuniformly sampled time series
Numerically Computing QCD Laplace Sum-Rules Using pySecDec
pySecDec is a program that numerically calculates dimensionally regularized
integrals. We use pySecDec to compute QCD Laplace sum-rules for pseudoscalar
(i.e., ) charmonium hybrids, and compare the results to
sum-rules computed using analytic results for dimensionally regularized
integrals. We find that the errors due to the use of numerical integration
methods is negligible compared to the uncertainties in the sum-rules stemming
from the uncertainties in the parameters of QCD, e.g., the coupling constant,
quark masses, and condensate values. Also, we demonstrate that numerical
integration methods can be used to calculate finite-energy and Gaussian
sum-rules in addition to Laplace sum-rules.Comment: 10 pages, 5 figure
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