Empirical modeling of the stellar spectrum of galaxies

An empirical method of modeling the stellar spectrum of galaxies is proposed, based on two successive applications of Principal Component Analysis (PCA). PCA is first applied to the newly available stellar library STELIB, supplemented by the J, H and K$_{s}$ magnitudes taken mainly from the 2 Micron All Sky Survey (2MASS). Next the resultant eigen-spectra are used to fit the observed spectra of a sample of 1016 galaxies selected from the Sloan Digital Sky Survey Data Release One (SDSS DR1). PCA is again applied, to the fitted spectra to construct the eigen-spectra of galaxies with zero velocity dispersion. The first 9 galactic eigen-spectra so obtained are then used to model the stellar spectrum of the galaxies in SDSS DR1, and synchronously to estimate the stellar velocity dispersion, the spectral type, the near-infrared SED, and the average reddening. Extensive tests show that the spectra of different type galaxies can be modeled quite accurately using these eigen-spectra. The method can yield stellar velocity dispersion with accuracies better than 10%, for the spectra of typical S/N ratios in SDSS DR1.Comment: 34 pages with 18 figures, submitted to A

Wolf-Rayet Galaxies in the Sloan Digital Sky Survey: the metallicity dependence of the initial mass function

We use a large sample of 174 Wolf-Rayet (WR) galaxies drawn from the Sloan Digital Sky Survey to study whether and how the slope of the stellar initial mass function depends on metallicity. We calculate for each object its oxygen abundance according to which we divide our sample into four metallicity subsamples. For each subsample, we then measure three quantities: the equivalent width of \hb emission line, the equivalent width of WR bump around 4650\AA, and the WR bump-to-\hb intensity ratio, and compare to the predictions of the same quantities by evolutionary synthesis models of Schaerer & Vacca. Such comparisons lead to a clear dependence of the slope of initial mass function ($\alpha$) on metallicity in that galaxies at higher metallicities tend to have steeper initial mass functions, with the slope index ranging from $\alpha\sim$1.00 for the lowest metallicity of $Z=0.001$ to $\alpha\sim$3.30 for the highest metallicity $Z=0.02$. We have carefully examined the possible sources of systematic error either in models or in our observational measurements and shown that these sources do not change this result.Comment: 12 pages, 6 figures, ApJ accepte

Chiral Antioxidant-based Gold Nanoclusters Reprogram DNA Epigenetic Patterns

Epigenetic modifications sit ‘on top of’ the genome and influence DNA transcription, which can force a significant impact on cellular behavior and phenotype and, consequently human development and disease. Conventional methods for evaluating epigenetic modifications have inherent limitations and, hence, new methods based on nanoscale devices are needed. Here, we found that antioxidant (glutathione) chiral gold nanoclusters induce a decrease of 5-hydroxymethylcytosine (5hmC), which is an important epigenetic marker that associates with gene transcription regulation. This epigenetic change was triggered partially through ROS activation and oxidation generated by the treatment with glutathione chiral gold nanoclusters, which may inhibit the activity of TET proteins catalyzing the conversion of 5-methylcytosine (5mC) to 5hmC. In addition, these chiral gold nanoclusters can downregulate TET1 and TET2 mRNA expression. Alteration of TET-5hmC signaling will then affect several downstream targets and be involved in many aspects of cell behavior. We demonstrate for the first time that antioxidant-based chiral gold nanomaterials have a direct effect on epigenetic process of TET-5hmC pathways and reveal critical DNA demethylation patterns

Notch effect on structural strength of components at elevated temperature under creep, fatigue and creep-fatigue loading conditions : phenomenon and mechanism

Structural discontinuities (e.g., nozzle, hole, and groove) widely occur in many high temperature components of nuclear and fossil power plants. In general, the notched component is used for simplified tests and analyses due to the complexity of the introduction of a practical component. In the previous work, the effects of the notch on failure life of the components have been reported experimentally, including the strengthening and weakening effects; however, the internal mechanisms have not been clearly demonstrated. This work reviews the notch effects on the structural strength of the notched components at elevated temperatures under creep, fatigue, and creep-fatigue loading conditions. Experimental phenomena (i.e., strengthening or weakening effects) for typical notched specimens subjected to the above three loading conditions are summarized, and the related factors for notch effects on creep rupture life or cycle to failure of the components are discussed. The mechanisms for the strengthening or weakening effects induced by a notch are described. Evaluation procedures for notch effect analysis under complex loading conditions are also included, and the primary challenges concerning the notch effect are provided for further investigations

Iron(II)-Catalyzed Intermolecular Amino-Oxygenation of Olefins through the N−O Bond Cleavage of Functionalized Hydroxylamines

An iron-catalyzed diastereoselective intermolecular olefin amino-oxygenation reaction is reported, which proceeds via an iron-nitrenoid generated by the N− O bond cleavage of a functionalized hydroxylamine. In this reaction, a bench-stable hydroxylamine derivative is used as the amination reagent and oxidant. This method tolerates a range of synthetically valuable substrates that have been all incompatible with existing amino-oxygenation methods. It can also provide amino alcohol derivatives with regio- and stereochemical arrays complementary to known amino-oxygenation methods

FeII and FeI emission in IRAS 07598+6508 and PHL 1092

One of the puzzles in understanding the spectra of active galactic nuclei (AGN) is the origin of the FeII emission. FeI emission, if present, will help reveal the physical conditions of the emitting gas. In an attempt to verify the presence of FeI lines, high S/N spectra of two FeII-strong quasars, IRAS 07598-6508 and PHL 1092, were obtained at the Multiple Mirror Telescope and the Steward 2.3 m Telescope. We have identified emission lines of FeI and TiII. The source of energy for FeII, FeI and TiII emission is probably not from ionization by the photon continuum, but heat. The high rate of energy generation and the presence of both high and low velocity gas indicate that the heat is generated not over a large area, but a narrow band in accretion disk, in which the rotational speed decreases rapidly.Comment: 17 pages, Latex, figures available upon request, to appear in Ap

Potassium zinc borate, KZnB3O6

The title compound, KZnB3O6 contains a remarkable [B6O12]6− group ( symmetry) formed by two rings linked by edge-sharing BO4 tetra­hedra, a feature that has only been observed previously under high pressure conditions. These borate groups are connected through distorted ZnO4 tetra­hedra in edge-shared pairs ( symmetry), forming a three-dimensional network whose cavities are filled by K+ cations

catena-Poly[[triaqua­(pyridine-κN)nickel(II)]-μ-sulfato-κ2 O:O′]

The title compound, [Ni(SO4)(C5H5N)(H2O)3]n, was synthesized by the hydro­thermal reaction of NiSO4·6H2O, pyridine and water. The central NiII atom is coordinated in a distorted octa­hedral environment by a pyridine N atom, three aqua O atoms and two O atoms of bridging sulfate anions, yielding a zigzag chain. A three-dimensional network is generated via complex hydrogen bonds involving the sulfate and aqua ligands and a pyridine C—H group