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