2,548 research outputs found
Search for associations containing young stars (SACY) VII. New stellar and substellar candidate members in the young associations
The young associations offer us one of the best opportunities to study the
properties of young stellar and substellar objects and to directly image
planets thanks to their proximity (200 pc) and age (5-150 Myr).
However, many previous works have been limited to identifying the brighter,
more active members (1 M) owing to photometric survey
sensitivities limiting the detections of lower mass objects. We search the
field of view of 542 previously identified members of the young associations to
identify wide or extremely wide (1000-100,000 au in physical separation)
companions. We combined 2MASS near-infrared photometry (, , ) with
proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the
field of view of known members. We collated further photometry and spectroscopy
from the literature and conducted our own high-resolution spectroscopic
observations for a subsample of candidate members. This complementary
information allowed us to assess the efficiency of our method. We identified 84
targets (45: 0.2-1.3 M, 17: 0.08-0.2 M, 22: 0.08 M)
in our analysis, ten of which have been identified from spectroscopic analysis
in previous young association works. For 33 of these 84, we were able to
further assess their membership using a variety of properties (X-ray emission,
UV excess, H, lithium and K I equivalent widths, radial velocities,
and CaH indices). We derive a success rate of 76-88% for this technique based
on the consistency of these properties. Once confirmed, the targets identified
in this work would significantly improve our knowledge of the lower mass end of
the young associations. Additionally, these targets would make an ideal new
sample for the identification and study of planets around nearby young stars.Comment: 28 pages, 24 figures, accepted in A&
Diagnóstico Prénatal de Hemocromatose Neonatal: Será possÃvel?
Introdução: A Hemocromatose Neonatal é uma doença hepática rara de inÃcio intrauterino, definida por insuficiência hepática neonatal associada a siderose extra-hepática. A doença hepática gestacional aloimune foi estabelecida como causa da lesão hepática fetal. Atualmente, não existe uma abordagem eficaz para o diagnóstico prénatal.
Caso ClÃnico: Grávida de 23 anos apresentou à s 32 semanas de gestação oligohidrâmnios e focos hepáticos hiperecogénicos. O recém-nascido prematuro desenvolveu falência orgânica multissistémica e faleceu ao segundo dia de vida, apesar de cuidados de suporte intensivos. A autópsia permitiu o diagnóstico de Hemocromatose Neonatal.
Conclusão: A identificação ecográfica de focos nodulares hiperecogénicos no fÃgado fetal pode ser sugestiva de Hemocromatose Neonatal. Investigações adicionais são necessárias para identificar o complexo aloimunitário especÃfico no sangue materno. O estabelecimento do diagnóstico num feto ou recém- -nascido afetado pode ter um grande impacto no prognóstico da doença e no desfecho de futuras gravidezes
Investigating Ca II emission in the RS CVn binary ER Vulpeculae using the Broadening Function Formalism
The synchronously rotating G stars in the detached, short-period (0.7 d),
partially eclipsing binary, ER Vul, are the most chromospherically active
solar-type stars known. We have monitored activity in the Ca II H & K reversals
for almost an entire orbit. Rucinski's Broadening Function Formalism allows the
photospheric contribution to be objectively subtracted from the highly blended
spectra. The power of the BF technique is also demonstrated by the good
agreement of radial velocities with those measured by others from less crowded
spectral regions. In addition to strong Ca II emission from the primary and
secondary, there appears to be a high-velocity stream flowing onto the
secondary where it stimulates a large active region on the surface 30 - 40
degrees in advance of the sub-binary longitude. A model light curve with a spot
centered on the same longitude also gives the best fit to the observed light
curve. A flare with approximately 13% more power than at other phases was
detected in one spectrum. We suggest ER Vul may offer a magnified view of the
more subtle chromospheric effects synchronized to planetary revolution seen in
certain `51 Peg'-type systems.Comment: Accepted to AJ; 17 pages and 16 figure
On the binary nature of 1RXS J162848.1-415241
We present spectroscopy of the optical counterpart to 1RXS J162848.1-41524,
also known as the microquasar candidate MCQC J162847-4152. All the data
indicate that this X-ray source is not a microquasar, and that it is a
single-lined chromospherically active binary system with a likely orbital
period of 4.9 days. Our analysis supports a K3IV spectral classification for
the star, which is dominant at optical wavelengths. The unseen binary component
is most likely a late-type (K7-M) dwarf or a white dwarf. Using the high
resolution spectra we have measured the K3 star's rotational broadening to be
vsini = 43 +/- 3 km/s and determined a lower limit to the binary mass ratio of
q(=M2/M1)>2.0. The high rotational broadening together with the strong CaII H &
K / Halpha emission and high-amplitude photometric variations indicate that the
evolved star is very chromospherically active and responsible for the
X-ray/radio emission.Comment: 15 pages, 5 figures, accepted for publication in Ap
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Morphological effects on the photocatalytic properties of SnO<inf>2</inf> nanostructures
The photocatalytic properties of SnO2 nanocrystals are tuned by varying their morphology and microstructure. SnO2 nanoparticles and nanowedges have been synthesised using hydrothermal methods, while microwave irradiation techniques have given nanospheres. Detailed structural and chemical characterization of these different morphologies has been accomplished. The influence of SnO2 morphology on photocatalytic activity has been examined by monitoring the degradation of aqueous methylene blue dye. Results demonstrate that changing the morphology of the SnO2 modulates both surface area and levels of surface defects and that these alterations are reflected in the photocatalytic properties of the materials. The degradation of methylene blue dye (98%) in the presence of SnO2 nanoparticles under simulated solar irradiation is superior to previously reported photocatalyst performance and is comparable to that of standard TiO2 (Degussa P-25). The SnO2 nanoparticles perform better than both the nanowedges and nanospheres and this is attributed to the number of surface defects available to the high surface area material. They also reveal outstanding recyclability and stability
Biosorption of nickel, cobalt, zinc and copper ions by Serratia marcescens strain 16 in mono and multimetallic systems
The metallurgical industry is one of the main sources of heavy metal pollution, which represents a severe threat to life. Metals can be removed from aqueous solutions by using microbial biomasses. This paper analyses the heavy metal biosorption capacity of Serratia marcescens strain 16 in single and multimetallic systems. The results obtained show that Co(II), Ni(II) and Zn(II) biosorption in monometallic systems is two to three times higher than in the presence of bi-metallic and multimetallic solutions. Fourier transform infrared spectroscopy confirmed that carbonyl, carboxyl and hydroxyl were the main functional groups, as well as the amide bands I and II involved in metal uptake, which are present in external structures of the bacterial cell. The results obtained demonstrated the viability of S. marcescens strain 16 as a biosorbent for the design of eco-friendly technologies for the treatment of waste liquor.The authors would like to acknowledge the financial support provided by the Iberoamerican PhD Program (UCA-UH), the AUIP and by the International Foundation of Science (Grant C/4078-2)
Optimization of nickel and cobalt biosorption by native Serratia marcescens strains isolated from serpentine deposits using response surface methodology
The treatment of metal-polluted wastes is a challenging issue of environmental concern. Metals can be removed using microbial biomass, and this is an interesting approach towards the design of eco-friendly technologies for liquid waste treatment. The study reported here aimed to optimize nickel and cobalt biosorption from aqueous solutions using three native metal-resistant Serratia marcescens strains. Ni(II) and Co(II) biosorption by S. marcescens strains was found to fit better to Langmuir's model, with maximum uptake capacities of 13.5 mg g(-1) for Ni(II) ions and 19.9 mg g(-1) for Co(II) ions. Different experimental conditions of initial metal concentration, pH, initial biomass, and temperature were optimized using the Plackett-Burman method, and, finally, biomass and metal concentration were studied using the response surface methodology (RSM) to improve biosorption. The optimum uptake capacities for Co(II) ions by the three biosorbents used were obtained for initial metal concentrations of 35-40 mg L-1 and an initial biomass of 6 mg. For Ni(II) ions, the optimum uptake capacity was achieved with 1 mg of initial biomass for S. marcescens C-1 and C-19, and with 7 mg for S. marcescens C-16, with initial concentrations of 20-50 mg L-1. The results obtained demonstrate the viability of native S. marcescens strains as biosorbents for Ni(II) and Co(II) removal. This study also contributes to our understanding of the potential uses of serpentine microbial populations for the design of environmental cleanup technologies
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