1,236 research outputs found
Methods of Hierarchical Clustering
We survey agglomerative hierarchical clustering algorithms and discuss
efficient implementations that are available in R and other software
environments. We look at hierarchical self-organizing maps, and mixture models.
We review grid-based clustering, focusing on hierarchical density-based
approaches. Finally we describe a recently developed very efficient (linear
time) hierarchical clustering algorithm, which can also be viewed as a
hierarchical grid-based algorithm.Comment: 21 pages, 2 figures, 1 table, 69 reference
Online Medical Data Stream Mining Based on Adaptive Neuro-Fuzzy Approaches
The purpose of the paper is to develop approach, based on adaptive neuro-fuzzy systems to solve the tasks of medical data stream mining in online-mode. Results. As a result, approbation of the developed approach in supervised learning mode using multidimensional neo-fuzzy neuron on medical data of patients with urological disease was investigated.Метою статті є розроблення підходу, основаного на адаптивних нейро-фаззі системах, для розв’язання завдань оброблення потоків медичних даних в онлайн-режимі. Результати. Проведено апробацію розробленого підходу в режимі контрольованого навчання за допомоги багатовимірного нео-фаззі нейрона з використанням медичних даних пацієнтів з урологічними захворюваннями.Цель статьи — разработка подхода, основанного на адаптивных нейро-фаззи системах, для решения задач обработки потоков медицинских данных в онлайн-режиме. Результаты. Проведена апробация разработанного подхода в режиме контролируемого обучения с применением многомерного нео-фаззи нейрона при использовании медицинских данных пациентов с урологическими заболеваниями
Representing complex data using localized principal components with application to astronomical data
Often the relation between the variables constituting a multivariate data
space might be characterized by one or more of the terms: ``nonlinear'',
``branched'', ``disconnected'', ``bended'', ``curved'', ``heterogeneous'', or,
more general, ``complex''. In these cases, simple principal component analysis
(PCA) as a tool for dimension reduction can fail badly. Of the many alternative
approaches proposed so far, local approximations of PCA are among the most
promising. This paper will give a short review of localized versions of PCA,
focusing on local principal curves and local partitioning algorithms.
Furthermore we discuss projections other than the local principal components.
When performing local dimension reduction for regression or classification
problems it is important to focus not only on the manifold structure of the
covariates, but also on the response variable(s). Local principal components
only achieve the former, whereas localized regression approaches concentrate on
the latter. Local projection directions derived from the partial least squares
(PLS) algorithm offer an interesting trade-off between these two objectives. We
apply these methods to several real data sets. In particular, we consider
simulated astrophysical data from the future Galactic survey mission Gaia.Comment: 25 pages. In "Principal Manifolds for Data Visualization and
Dimension Reduction", A. Gorban, B. Kegl, D. Wunsch, and A. Zinovyev (eds),
Lecture Notes in Computational Science and Engineering, Springer, 2007, pp.
180--204,
http://www.springer.com/dal/home/generic/search/results?SGWID=1-40109-22-173750210-
Photospheric and chromospheric activity on the young solar-type star HD 171488
We present the results of contemporaneous spectroscopic and photometric
monitoring of the young solar-type star HD171488 (Prot~1.337 d) aimed at
studying surface inhomogeneities at photospheric/chromospheric levels. Echelle
FOCES spectra (R~40000) and Johnson photometry have been performed in 2006.
Spectral type, rotational velocity, metallicity, and gravity were determined
using a code developed by us. The metallicity was measured from the analysis of
iron lines. The spectral subtraction technique was applied to the most relevant
chromospheric diagnostics included in the FOCES spectral range (CaII IRT,
Halpha, HeI-D3, Hbeta, CaII H&K). A model with two large high-latitude spots is
sufficient to reproduce the B/V light curves and the radial velocity
modulation, if a temperature difference between photosphere and spots of 1500 K
is used. A Doppler imaging analysis of photospheric lines confirms a similar
spot distribution. With the help of an analogous geometric two-spot model, we
are able to reproduce the modulations in the residual chromospheric emissions
adopting different values of ratios between the flux of plages and quiet
chromosphere (5 for Halpha and 3 for CaII). Facular regions of solar type
appear to be the main responsible for the modulations of chromospheric
diagnostics. Both the spot/plage model and the cross-correlation between the
light curve and the chromospheric line fluxes display a lead effect of plages
with respect to spots (20-40 deg in longitude). The active regions of the
rapidly rotating star HD171488 are similar to the solar ones in some respect,
because the spot temperature is close to that of sunspot umbrae and the plage
flux-contrast is consistent with the average solar values. The main differences
with respect to the Sun are larger sizes and higher latitudes.Comment: Abstract shortened. 15 pages, 7 figures, 5 tables. Accepted for the
publication in Astronomy and Astrophysic
A novel face recognition system using hybrid neural and dual eigenspaces methods
2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
A new look at Spitzer primary transit observations of the exoplanet HD189733b
Blind source separation techniques are used to reanalyse two exoplanetary
transit lightcurves of the exoplanet HD189733b recorded with the IR camera IRAC
on board the Spitzer Space Telescope at 3.6m during the "cold" era. These
observations, together with observations at other IR wavelengths, are crucial
to characterise the atmosphere of the planet HD189733b. Previous analyses of
the same datasets reported discrepant results, hence the necessity of the
reanalyses. The method we used here is based on the Independent Component
Analysis (ICA) statistical technique, which ensures a high degree of
objectivity. The use of ICA to detrend single photometric observations in a
self-consistent way is novel in the literature. The advantage of our reanalyses
over previous work is that we do not have to make any assumptions on the
structure of the unknown instrumental systematics. Such "admission of
ignorance" may result in larger error bars than reported in the literature, up
to a factor . This is a worthwhile trade-off for much higher objectivity,
necessary for trustworthy claims. Our main results are (1) improved and robust
values of orbital and stellar parameters, (2) new measurements of the transit
depths at 3.6m, (3) consistency between the parameters estimated from the
two observations, (4) repeatability of the measurement within the photometric
level of in the IR, (5) no evidence of stellar
variability at the same photometric level within 1 year.Comment: 43 pages, 18 figure
Physical Parameters of Some Close Binaries: ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg
With the aim of providing new and up-to-date absolute parameters of some
close binary systems, new BVR CCD photometry was carried out at the Ankara
University Observatory (AUG) for five eclipsing binaries, ET Boo, V1123 Tau,
V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In
this paper, we present the orbital solutions for these systems obtained by
simultaneous light and radial velocity curve analyses. Extensive orbital
solution and absolute parameters for ET Boo system were given for the first
time through this study. According to the analyses, ET Boo is a detached binary
while the parameters of four remaining systems are consistent with the nature
of contact binaries. The evolutionary status of the components of these systems
are also discussed by referring to their absolute parameters found in this
study.Comment: this accepted paper will be published in New Astronom
A Comprehensive Characterization of the 70 Virgins Planetary System
An on-going effort in the characterization of exoplanetary systems is the accurate determination of host star properties. This effort extends to the relatively bright host stars of planets discovered with the radial velocity method. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is aiding in these efforts as part of its observational campaign for exoplanet host stars. One of the first known systems is that of 70 Virginis, which harbors a jovian planet in an eccentric orbit. Here we present a complete characterization of this system with a compilation of TERMS photometry, spectroscopy, and interferometry. We provide fundamental properties of the host star through direct interferometric measurements of the radius (1.5% uncertainty) and through spectroscopic analysis. We combined 59 new Keck HIRES radial velocity measurements with the 169 previously published from the ELODIE, Hamilton, and HIRES spectrographs, to calculate a refined orbital solution and construct a transit ephemeris for the planet. These newly determined system characteristics are used to describe the Habitable Zone of the system with a discussion of possible additional planets and related stability simulations. Finally, we present 19 years of precision robotic photometry that constrain stellar activity and rule out central planetary transits for a Jupiter-radius planet at the 5σ level, with reduced significance down to an impact parameter of b = 0.95
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