J-PLUS: Identification of low-metallicity stars with artificial neural networks using SPHINX

Whitten, D. D.,Placco, V. M.,Beers, T. C.,Chies-Santos, A. L.,Bonatto, C.,Varela, J.,Cristó,bal-Hornillos, D.,Ederoclite, A.,Masseron, T.,Lee, Y. S.,Akras, S.,Borges Fernandes, M.,Caballero, J. Springer-Verlag 2019 Astronomy and astrophysics Vol.622 No.-

<P><I>Context.</I> We present a new methodology for the estimation of stellar atmospheric parameters from narrow- and intermediate-band photometry of the Javalambre Photometric Local Universe Survey (J-PLUS), and propose a method for target pre-selection of low-metallicity stars for follow-up spectroscopic studies. Photometric metallicity estimates for stars in the globular cluster M15 are determined using this method.</P><P><I>Aims.</I> By development of a neural-network-based photometry pipeline, we aim to produce estimates of effective temperature, <I>T</I>eff, and metallicity, [Fe/H], for a large subset of stars in the J-PLUS footprint.</P><P><I>Methods.</I> The Stellar Photometric Index Network Explorer, SPHINX, was developed to produce estimates of <I>T</I>eff and [Fe/H], after training on a combination of J-PLUS photometric inputs and synthetic magnitudes computed for medium-resolution (<I>R</I> ~ 2000) spectra of the Sloan Digital Sky Survey. This methodology was applied to J-PLUS photometry of the globular cluster M15.</P><P><I>Results.</I> Effective temperature estimates made with J-PLUS Early Data Release photometry exhibit low scatter, σ(<I>T</I>eff) = 91 K, over the temperature range 4500 < <I>T</I>eff (K) < 8500. For stars from the J-PLUS First Data Release with 4500 < <I>T</I>eff (K) < 6200, 85 ± 3% of stars known to have [Fe/H] < −2.0 are recovered by SPHINX. A mean metallicity of [Fe/H] = − 2.32 ± 0.01, with a residual spread of 0.3 dex, is determined for M15 using J-PLUS photometry of 664 likely cluster members.</P><P><I>Conclusions.</I> We confirm the performance of SPHINX within the ranges specified, and verify its utility as a stand-alone tool for photometric estimation of effective temperature and metallicity, and for pre-selection of metal-poor spectroscopic targets.</P>

Self-doped Carboxylated Polyaniline: Effect of Hydrogen Bonding on the Doping of Polymers

Kim, Seong-Cheol,Whitten, James,Kumar, Jayant,Bruno, Ferdinando F.,Samuelson, Lynne A. The Polymer Society of Korea 2009 Macromolecular Research Vol.17 No.9

This study examined the unique self-doping behavior of carboxylated polyaniline (PCA). The self-doped PCA was synthesized using an environmentally benign enzymatic polymerization method with cationic surfactants. XPS showed that HCl-doped PCA contained approximately 34% of protonated amines but self-doped PCA contained 9.6% of the doped form of nitrogen at pH 4. FTIR and elemental analysis showed that although the PCA was doped with the proton of strong acids at low pH via the protonation of amines, the self-doping mechanism of PCA at pH > 4 was mainly due to hydrogen bonding between the carboxylic acid group and amine group.

Self-doped Carboxylated Polyaniline

Seong Cheol Kim,Jemes Whitten,Jayant Kumar,Ferdinando F. Bruno,Lyunne A. Samuelson 한국고분자학회 2009 Macromolecular Research Vol.17 No.9

Photodecomposition of Ti Compounds

Shin, Dong Myung,Whitten, David G. 弘益大學校 科學技術硏究所 1991 科學技術硏究論文集 Vol.1 No.-

Ti 화합물의 광분해 반응을 불소핵자기공명 기술을 이용하여 그 반응기작을 밝혀 보았다. Titanocene은 Ti과 페닐기가 끊어지면서 라디칼을 형성하거나, 두 개의 페닐기가 환원적 제거반응(elimination)과정을 따라서 분해된다고 알려져 있다. 본 연구에서는 bis(phenyl-F?) bis (?-cyclopentadienyl) titanium(Ⅳ)을 사용하였으며, 이 물질은 균일결합분해과정(homolitic bond dissociation process)을 거쳐서 라디칼을 형성하는 것을 규명하였다.

스쿠알렌 집합체의 광전기화학적 효과에 관한 연구

Young Soon Kim,Kock-Yee Law,David G. Whitten 대한화학회 1993 대한화학회지 Vol.37 No.7

순수 정제한 스쿠알렌 색소(DSSQ(4-distearylamino phenyl-4'-dimethylaminophenylsquaraine) 를 Langmuir Blodgett 방법으로 $SnO_2$ 전극위에 단분자막으로 도포하였다. DSSQ 용액의 최대 흡수 파장은 630 nm 이었으나, $SnO_2$ 전극에 도포한 상태는 최대흡광파장 위치가 530 nm로 이동되어 스쿠알렌 집합체를 나타내었다. 이 집합체를 열처리하였더니 최대흡광 위치는 620~680 nm 로 이동되었다. 스쿠알렌 집합체에서의 에너지 이동 관계를 알기 위하여 광전류를 측정하였다. 광전류의 action spectrum은 흡수스펙트럼과 거의 같은 경향을 보였으며, 열처리한 시료의 광전류 action 스펙트럼도 처리전과 같은 결과를 나타내었다. 이때의 양자수율은 약 0.3%이었다. 용액내의 빛의 tunneling 효과를 보기 위하여 $SnO_2$전극과 DSSQ 색소사이에 스테아린산을 2~8층으로 각각 도포하고 광전류를 측정하였더니, 광전류가 현저히 감소하였다. 2층을 더 도포한 시료에서는 광전류가 전혀 나타나지 않았다. 또한 전해질 용액에 질소를 통하였을 경우에는 광기전력이 현저히 감소하고, 산소를 통하였을 때는 같은 정도로 증가하는 것으로 보아 전해질의 용존 산소가 전자 주게 역할을 하고 있음을 추정할 수 있었다. Monolayers of pure surfactant squaraine, DSSQ(4-distearyl amino phenyl-4'-dimethylaminophenylsquaraine), were deposited on $SnO_2 $ electrodes by the Langmuir-Blodgett film technique. The DSSQ film exhibits ${\lambda}_{max}$ at ∼530 nm. The absorption is significantly red-shifted from the solution of DSSQ (633 nm in chloroform), suggesting that the squaraine chromophores form aggregates in the LB film. The photogeneration of the squaraine aggregates is studied by measuring the photocurrents in photoelectrochemical cells consisting of the squaraine of the aggregates is found to parallel its absorption spectrum and quantum efficiency as high as 0.3% has been observed. While the photocurrent was attenuated exponentially when stearic acid layers (up to 8 layers) are inserted between the squaraine layer and the electrode, it is nearly extinguished when the squaraine layer is over-coated with 2 layers of stearic acid. A model for the observation is proposed and the roles of the electrolytes and oxygen on the photogeneration process will be discussed.

Light and dark biocidal activity of cationic poly(arylene ethynylene) conjugated polyelectrolytes

Corbitt, Thomas S.,Ding, Liping,Ji, Eunkyung,Ista, Linnea K.,Ogawa, Katsu,Lopez, Gabriel P.,Schanze, Kirk S.,Whitten, David G. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.7

In this paper we report a study of cationic poly(arylene ethynylene) conjugated polyelectrolytes. The objective of the study was to compare the behavior of a polymer where a thiophene has replaced a phenyl ring in poly(phenylene ethynylene) polycations (PPE) previously investigated. Properties of solution phase and physisorbed suspensions of the polymer on microspheres were investigated. The photophysical properties of the polymer are evaluated and used to understand the striking differences in biocidal activity compared to the PPE polymers previously examined. The principal findings are that the thiophene polymer has remarkable dark biocidal activity against Pseudomonas aeruginosa strain PAO1 but very little light-activated activity. The low light-activated biocidal activity of the thiophene polymer is attributed to a highly aggregated state of the polymer in aqueous solutions and on microspheres as a physisorbed coating. This results in low triplet yields and a very poor sensitization of singlet oxygen and other reactive oxygen intermediates. The highly effective dark biocidal activity of the thiophene-containing polymers is attributed to its high lipophilicity and the presence of accessible quaternary ammonium groups. The difference in behavior among the polymers compared provides insights into the mechanism of the dark process and indicates that aggregation of polymer can reduce light activated biocidal activity by suppressing singlet oxygen generation.

Tough Supersoft Sponge Fibers with Tunable Stiffness from a DNA Self-Assembly Technique

Lee, Chang Kee,Shin, Su Ryon,Mun, Ji Young,Han, Sung-Sik,So, Insuk,Jeon, Ju-Hong,Kang, Tong Mook,Kim, Sun I.,Whitten, Philip G,Wallace, Gordon G.,Spinks, Geoffrey M.,Kim, Seon Jeong WILEY-VCH Verlag 2009 Angewandte Chemie. international edition Vol.48 No.28

<P>Tough and soft: Highly porous, spongelike materials self-assemble by calcium ion condensation of DNA-wrapped carbon nanotubes (SWNTs–DNA; see picture, IL=ionic liquid). The toughness, modulus, and swellability of the electrically conductive sponges can be tuned by controlling the density and strength of interfiber junctions. The sponges have compliances similar to the softest natural tissue, while robust interfiber junctions give high toughness. <img src='wiley_img/14337851-2009-48-28-ANIE200804788-content.gif' alt='wiley_img/14337851-2009-48-28-ANIE200804788-content'> </P> <B>Graphic Abstract</B> <P>Tough and soft: Highly porous, spongelike materials self-assemble by calcium ion condensation of DNA-wrapped carbon nanotubes (SWNTs–DNA; see picture, IL=ionic liquid). The toughness, modulus, and swellability of the electrically conductive sponges can be tuned by controlling the density and strength of interfiber junctions. The sponges have compliances similar to the softest natural tissue, while robust interfiber junctions give high toughness. <img src='wiley_img/14337851-2009-48-28-ANIE200804788-content.gif' alt='wiley_img/14337851-2009-48-28-ANIE200804788-content'> </P>