9,694 research outputs found
On using block principal component analysis for reducing gene-expression data dimensions
Since a microarray gene expression database contains a large number of variables and a relatively small number of samples, using and analyzing the databases require an intense, large-dimension computation method. Principal component analysis (PCA) is a useful tool to reduce the number of dimensions, and therefore, the complexity. PCA allows us to analyze the gene expression database with a relatively small data dimension without losing relevant information and increases the analytic visibility of the data. The initial computation using PCA, however, involves calculating a high-dimension covariance or correlation matrix and requires time and hardware resources which are limited in most real situations; In this thesis, we propose to use a Block Principal Component Analysis (Block PCA) method, introduced by Liu et al. (2002), to produce a subset that can explain a large amount of variation and propose criterion to find the most appropriate subsets; The gene expression data typically is highly correlated and the covariance matrix becomes highly ill-conditioned. The Mahalanobis distances resulting from the application of software packages such as SAS are not reliable in such cases. We investigate the effect of ill-conditioning on Discriminant Analysis of gene expression data from a DNA microarray. Bioinformatics literature recommends forming blocks of variables that are correlated with another. We proposed the method of Partial Least Square (PLS) to form the block of correlated variables for use in Block PCA
P-Cygni Type Lya from Starburst Galaxies
P-Cygni type Lya profiles exhibited in nearly half of starburst galaxies,
both nearby and high-z, are believed to be formed by an expanding supershell
surrounding a star-forming region. We apply the Monte Carlo code which was
developed previously for static and plane-parallel medium to calculate the Lya
line transfer in a supershell of neutral hydrogen which are expanding radially
in a spherical bulk flow. We consider typical cases that the supershell has the
Lya line-centre optical depth of , a radial expansion
velocity of \tau_0$ and V_exp of the
supershell. We discuss the effects of dust extinction and the implication of
our works in relation to recent spectroscopic observations of starburst
galaxies.Comment: 15 pages, 6 figures, submitted to MNRA
Highly efficient source for frequency-entangled photon pairs generated in a 3rd order periodically poled MgO-doped stoichiometric LiTaO3 crystal
We present a highly efficient source for discrete frequency-entangled photon
pairs based on spontaneous parametric down-conversion using 3rd order type-0
quasi-phase matching in a periodically poled MgO-doped stoichiometric LiTaO3
crystal pumped by a 355.66 nm laser. Correlated two-photon states were
generated with automatic conservation of energy and momentum in two given
spatial modes. These states have a wide spectral range, even under small
variations in crystal temperature, which consequently results in higher
discreteness. Frequency entanglement was confirmed by measuring two-photon
quantum interference fringes without any spectral filtering.Comment: 4 pages, 4 figures, to be published in Optics Letter
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