13,125 research outputs found
Mixtures of Common Skew-t Factor Analyzers
A mixture of common skew-t factor analyzers model is introduced for
model-based clustering of high-dimensional data. By assuming common component
factor loadings, this model allows clustering to be performed in the presence
of a large number of mixture components or when the number of dimensions is too
large to be well-modelled by the mixtures of factor analyzers model or a
variant thereof. Furthermore, assuming that the component densities follow a
skew-t distribution allows robust clustering of skewed data. The alternating
expectation-conditional maximization algorithm is employed for parameter
estimation. We demonstrate excellent clustering performance when our model is
applied to real and simulated data.This paper marks the first time that skewed
common factors have been used
Anisotropic multiple bounce models
We analyze the Galileon ghost condensate implementation of a bouncing
cosmological model in the presence of a non negligible anisotropic stress. We
exhibit its structure, which we find to be far richer than previously thought.
In particular, even restricting attention to a single set of underlying
microscopic parameters, we obtain, numerically, many qualitatively different
regimes: depending on the initial conditions on the scalar field leading the
dynamics of the universe, the contraction phase can evolve directly towards a
singularity, avoid it by bouncing once, or even bounce many times before
settling into an ever-expanding phase. We clarify the behavior of the
anisotropies in these various situations.Comment: 11 pages, 9 figures, minor correction
Mixtures of Skew-t Factor Analyzers
In this paper, we introduce a mixture of skew-t factor analyzers as well as a
family of mixture models based thereon. The mixture of skew-t distributions
model that we use arises as a limiting case of the mixture of generalized
hyperbolic distributions. Like their Gaussian and t-distribution analogues, our
mixture of skew-t factor analyzers are very well-suited to the model-based
clustering of high-dimensional data. Imposing constraints on components of the
decomposed covariance parameter results in the development of eight flexible
models. The alternating expectation-conditional maximization algorithm is used
for model parameter estimation and the Bayesian information criterion is used
for model selection. The models are applied to both real and simulated data,
giving superior clustering results compared to a well-established family of
Gaussian mixture models
A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656
We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656.
X-ray emission from the NLS1 galaxy undergoes long-term variability with
0.1--2.0 keV flux changing by a factor of 2 within about 3 yr. The ROSAT PSPC
spectrum of RXJ1236.9+2656 is well represented by a power-law of Gamma = 3.7
absorbed by matter in our own Galaxy (N_H = 1.33X10^20 cm**-2). Intrinsic soft
X-ray luminosity of the NLS1 galaxy is estimated to be 1.5X10^43 erg/s in the
energy band of 0.1-2.0 keV. The optical spectrum of RXJ1236.9+2656 is typical
of NLS1 galaxies and shows narrow Balmer emission lines (1100 km/s < FWHM <
1700 km/s) of Hbeta, Halpha, and forbidden lines of [O III] and [N II]. Fe II
multiplets, usually present in optical spectra of NLS1 galaxies, are also
detected in RXJ1236.9+2656.Comment: 4 pages, A&A style Latex, To apear in A&A as a research not
Hubungan antara Kualitas Produk dan Kepuasan Konsumen dengan Word Of Mouth Communication pada Mahasiswa Pengguna Blackberry di Universitas Surabaya
BlackBerry merupakan salah satu jenis smartphone yang sedang digandrungi masyarakat di Indonesia. Walaupun pemasaran BlackBerry tidak melalui media konvensional seperti media iklan maupun cetak, namun pengguna BlackBerry di Indonesia mencapai 300- 400 ribu pelanggan dan diproyeksi akan menjadi yang terbanyak di seluruh dunia dalam waktu dekat. Ketertarikan pada BlackBerry juga terjadi pada mahasiswa di Universitas Surabaya. Survey awal menyebutkan bahwa para mahasiswa tersebut mendapatkan informasi melalui word of mouth (WOM). Word of mouth communication (WOM) sendiri merupakan sebuah proses pengaruh perseorangan dimana terjadi komunikasi dari dalam antara pemberi dan penerima pesan yang dapat merubah perilaku dan sikap dari sang penerima. Dalam penelitian ini, WOM akan dilihat korelasinya dengan kualitas produk dan kepuasan konsumen. Penelitian ini merupakan penelitian kuantitatif uji korelasional yang melibatkan 200 mahasiswa Universitas Surabaya yang berusia 19-22 tahun dan menggunakan produk BlackBerry. Sampel penelitian diambil dengan menggunakan teknik incidental sampling dan data yang diperoleh akan dianalisis menggunakan uji korelasi non-parametrik kendall\u27s spearman. Hasil penelitian menunjukkan bahwa terdapat hubungan yang signifikan antara kualitas produk dan kepuasan konsumen dengan word of mouth communication. Adapun aspek yang mendominasi dari kualitas produk ialah style (desain/penampilan) dan features (fitur), sedangkan aspek yang mendominasi dari kepuasan konsumen ialah confirmations to spesifications, yang berbicara mengenai sejauh mana kinerja melebihi atau kurang dari ekspektasi dan harapan konsumen
Parsimonious Shifted Asymmetric Laplace Mixtures
A family of parsimonious shifted asymmetric Laplace mixture models is
introduced. We extend the mixture of factor analyzers model to the shifted
asymmetric Laplace distribution. Imposing constraints on the constitute parts
of the resulting decomposed component scale matrices leads to a family of
parsimonious models. An explicit two-stage parameter estimation procedure is
described, and the Bayesian information criterion and the integrated completed
likelihood are compared for model selection. This novel family of models is
applied to real data, where it is compared to its Gaussian analogue within
clustering and classification paradigms
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