Objective Identification of Informative Wavelength Regions in Galaxy Spectra

Understanding the diversity in spectra is the key to determining the physical parameters of galaxies. The optical spectra of galaxies are highly convoluted with continuum and lines which are potentially sensitive to different physical parameters. Defining the wavelength regions of interest is therefore an important question. In this work, we identify informative wavelength regions in a single-burst stellar populations model by using the CUR Matrix Decomposition. Simulating the Lick/IDS spectrograph configuration, we recover the widely used Dn(4000), Hbeta, and HdeltaA to be most informative. Simulating the SDSS spectrograph configuration with a wavelength range 3450-8350 Angstrom and a model-limited spectral resolution of 3 Angstrom, the most informative regions are: first region-the 4000 Angstrom break and the Hdelta line; second region-the Fe-like indices; third region-the Hbeta line; fourth region-the G band and the Hgamma line. A Principal Component Analysis on the first region shows that the first eigenspectrum tells primarily the stellar age, the second eigenspectrum is related to the age-metallicity degeneracy, and the third eigenspectrum shows an anti-correlation between the strengths of the Balmer and the Ca K and H absorptions. The regions can be used to determine the stellar age and metallicity in early-type galaxies which have solar abundance ratios, no dust, and a single-burst star formation history. The region identification method can be applied to any set of spectra of the user's interest, so that we eliminate the need for a common, fixed-resolution index system. We discuss future directions in extending the current analysis to late-type galaxies.Comment: 36 Pages, 13 Figures, 4 Tables. AJ Accepte

SiC epitaxial growth on Si(100) substrates using carbon tetrabromide

3C-SiC films were grown on Si by VPE using CBr4 as the carbon source, at temperatures ranging from 1100 to 1250?C. XRD, TEM, AFM, and SEM results indicate that the epitaxy proceeds as a 3D growth of uncoalesced islands at low temperature, whereas a continuous layer with hillocks on top is obtained above 1200?C. The shape and faceting of the islands are analyzed by AFM, showing (311) preferred facets.vedi abstract ingles

Building a Prototype for Network Measurement Virtual Observatory

Online sharing of scientific information has accelerated the research activity in various different domains of science. This fact inspires us to initiate this kind of approach in the field of network research and review some projects pointing towards this direction. Using the experiences of similar efforts in other domains of sciences we are building a prototype node for Network Measurement Virtual Observatory. The goal of the observatory is to stimulate network research through sharing available measurement data along with analysis results and providing easy-to-use “online ” network data analysis tools for network research and management purposes. We would also like to initiate discussion about standardization of network measurement data and to motivate other researchers to publish their own data and tools. In this paper we sketch the basic concept of Virtual Observatories and present a prototype system developed to share measurement data and tools associated with the ETOMIC measurement infrastructure