Influence of silver electrochemically deposited onto zinc oxide seed nanoparticles on the photoelectrochemical performance of zinc oxide nanorod films

Sem informaçãoThe present article examines the synthesis and characterization of zinc oxide nanorods grown on zinc oxide and silver nanoparticle seeds. Zinc oxide seeds were electrodeposited on a support of fluorine-doped tin oxide glass and heat-treated at 380 degrees C. Silver nanoparticles were then deposited on this substrate, which was heat-treated at 160 degrees C. Their presence was confirmed using ultraviolet-visible spectroscopy, by observing an absorption peak around 400 nm, corresponding to surface plasmon resonance. Growth of zinc oxide nanorods was achieved in a chemical bath at 90 degrees C. The obtained films were analyzed by cyclic voltammetry, X-ray diffraction, and scanning electron microscopy. They consisted of zinc oxide with a Wurtzite-type crystal structure, arranged as nanorods of 50 nm. X-ray photoelectron spectroscopy exhibits peaks attributed to silver (0) and to the formation of silver oxide on the silver nanoparticle surface. In addition, two types of oxygen (O 1 s) were observed: oxygen from the crystalline network (O-2) and chemisorbed oxygen (-OH), for the seed and the nanorod films, respectively. The nanorods grown on zinc oxide seeds with silver deposits had a round shape and greater photoactivity than those grown without silver. This difference is attributed to the additional reflection that silver provides to the light reaching the film, thereby increasing the photogeneration from the charge carriers.919Sem informaçãoSem informaçãoSem informaçãoThe author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the project no. 133-FINCYT-IB-2015 and no. 113-INNOVATE PERU-ISASS-2018. This work is partially supported by PICT 2014 2386

The first confirmation of V-type asteroids among the Mars crosser population

The Mars crossing region constitutes a path to deliver asteroids from the Inner Main Belt to the Earth crossing space. While both the Inner Main Belt and the population of Earth crossing asteroids contains a significant fraction of asteroids belonging to the V taxonomic class, only two of such V-type asteroids has been detected in the Mars crossing region up to now. In this work, we searched for asteroids belonging to the V class among the population of Mars crossing asteroids, in order to support alternative paths to the delivery of this bodies into the Earth crossing region. We selected 18 candidate V-type asteroids in the Mars crossing region using observations contained in the Sloan Digital Sky Survey Moving Objects Catalog. Then, we observed 4 of these candidates to take their visible spectra using the Southern Astrophysical Research Telescope (SOAR). We also performed the numerical simulation of the orbital evolution of the observed asteroids. We confirmed that 3 of the observed asteroids belong to the V class, and one of these may follow a path that drives it to an Earth collision in some tens of million years

Possible ring material around centaur (2060) Chiron

We propose that several short duration events observed in past stellar occultations by Chiron were produced by rings material. From a reanalysis of the stellar occultation data in the literature we determined two possible orientations of the pole of Chiron's rings, with ecliptic coordinates l=(352+/-10) deg, b=(37+/-10) deg or l=(144+/-10) deg, b=(24+/-10) deg . The mean radius of the rings is (324 +/- 10) km. One can use the rotational lightcurve amplitude of Chiron at different epochs to distinguish between the two solutions for the pole. Both imply lower lightcurve amplitude in 2013 than in 1988, when the rotational lightcurve was first determined. We derived Chiron's rotational lightcurve in 2013 from observations at the 1.23-m CAHA telescope and indeed its amplitude is smaller than in 1988. We also present a rotational lightcurve in 2000 from images taken at CASLEO 2.15-m telescope that is consistent with our predictions. Out of the two poles the l=(144+/-10) deg, b=(24+/-10) deg solution provides a better match to a compilation of rotational lightcurve amplitudes from the literature and those presented here. We also show that using this preferred pole, Chiron's long term brightness variations are compatible with a simple model that incorporates the changing brightness of the rings as the tilt angle with respect to the Earth changes with time. Also, the variability of the water ice band in Chiron's spectra in the literature can be explained to a large degree by an icy ring system whose tilt angle changes with time and whose composition includes water ice, analogously to the case of Chariklo. We present several possible formation scenarios for the rings from qualitative points of view and speculate on the reasons why rings might be common in centaurs. We speculate on whether the known bimodal color distribution of centaurs could be due to presence of rings and lack of them

Visible and near-infrared observations of asteroid 2012 DA14 during its closest approach of February 15, 2013

Near-Earth asteroid 2012 DA14 made its closest approach on February 15, 2013, when it passed at a distance of 27,700 km from the Earth's surface. It was the first time an asteroid of moderate size was predicted to approach that close to the Earth, becoming bright enough to permit a detailed study from ground-based telescopes. Asteroid 2012 DA14 was poorly characterized before its closest approach. We acquired data using several telescopes on four Spanish observatories: the 10.4m Gran Telescopio Canarias (GTC) and the 3.6m Telescopio Nazionale Galileo (TNG), both in the El Roque de los Muchachos Observatory (ORM, La Palma); the 2.2m CAHA telescope, in the Calar Alto Observatory (Almeria); the f/3 0.77m telescope in the La Hita Observatory (Toledo); and the f/8 1.5m telescope in the Sierra Nevada Observatory (OSN, Granada). We obtained visible and near-infrared color photometry, visible spectra and time-series photometry. Visible spectra together with color photometry of 2012 DA14 show that it can be classified as an L-type asteroid, a rare spectral type with a composition similar to that of carbonaceous chondrites. The time-series photometry provides a rotational period of 8.95 +- 0.08 hours after the closest approach, and there are indications that the object suffered a spin-up during this event. The large amplitude of the light curve suggests that the object is very elongated and irregular, with an equivalent diameter of around 18m. We obtain an absolute magnitude of H_R = 24.5 +- 0.2, corresponding to H_V = 25.0 +- 0.2. The GTC photometry also gives H_V = 25.29 +- 0.14. Both values agree with the value listed at the Minor Planet Center shortly after discovery. From the absolute photometry, together with some constraints on size and shape, we compute a geometric albedo of p_V = 0.44 +- 0.20, which is slightly above the range of albedos known for L-type asteroids (0.082 - 0.405).Comment: 7 pages, 4 figures, 1 table. Accepted in A&A (June 17 2013

J-PLUS: analysis of the intracluster light in the Coma cluster

The intracluster light (ICL) is a luminous component of galaxy clusters composed of stars that are gravitationally bound to the cluster potential but do not belong to the individual galaxies. Previous studies of the ICL have shown that its formation and evolution are intimately linked to the evolutionary stage of the cluster. Thus, the analysis of the ICL in the Coma cluster will give insights into the main processes driving the dynamics in this highly complex system. Using a recently developed technique, we measure the ICL fraction in Coma at several wavelengths, using the J-PLUS unique filter system. The combination of narrow- and broadband filters provides valuable information on the dynamical state of the cluster, the ICL stellar types, and the morphology of the diffuse light. We use the Chebyshev-Fourier Intracluster Light Estimator (CICLE) to disentangle the ICL from the light of the galaxies, and to robustly measure the ICL fraction in seven J-PLUS filters. We obtain the ICL fraction distribution of the Coma cluster at different optical wavelengths, which varies from $\sim 7\%-21\%$, showing the highest values in the narrowband filters J0395, J0410, and J0430. This ICL fraction excess is distinctive pattern recently observed in dynamically active clusters (mergers), indicating a higher amount of bluer stars in the ICL compared to the cluster galaxies. Both the high ICL fractions and the excess in the bluer filters are indicative of a merging state. The presence of younger/lower-metallicity stars the ICL suggests that the main mechanism of ICL formation for the Coma cluster is the stripping of the stars in the outskirts of infalling galaxies and, possibly, the disruption of dwarf galaxies during past/ongoing mergers.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in A&

Residential radon and characteristics of chronic obstructive pulmonary disease

It is not known whether residential radon exposure may be linked to the development of chronic obstructive pulmonary disease (COPD) and/or have an influence on the functional characteristics or exacerbations of COPD. The aim of this study was therefore to ascertain whether there might be an association between residential radon concentrations and certain characteristics of COPD. We analyzed COPD cases drawn from a case–control study conducted in an area of high radon exposure. Data were collected on spirometric pulmonary function variables, hospital admissions, and smoking. Radon measurements were taken using alpha-track-type CR-39 detectors individually placed in patients’ homes. All statistical analyses were performed using the IBM SPSS v22 computer software program. The study included 189 COPD cases (79.4% men; median age 64 years). The median radon concentration was 157 Bq/m3. No differences were found between radon concentration and sex, age or severity of breathing obstruction as measured by FEV1%. It should be noted, however, that 48.1% of patients with FEV1%  600 Bq/m3 exhibited no different characteristics in lung function. Exposure to radon does not appear to have an influence on the clinical characteristics of smokers and ex-smokers with COPD. As exposure to residential radon increases, there is no trend towards a worsening of FEV1%. Further studies are thus needed to analyze this possible association in never-smokers with COPDSpanish Society of Pneumology & Thoracic Surgery (Sociedad Española de Neumología y Cirugía Torácica—SEPAR), competitive Project Number 439, call 2018S

Composition of KBO (50000) Quaoar

Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune-the new frontiers of the Solar System-and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body. Methods. We present new near-infrared (3.6 and 4.5 mu m) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 mu m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range-from 0.3 to 4.5 mu m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H(2)O ice making use of the crystalline feature at 1.65 mu m. Results. We present a model confirming previous results regarding the presence of crystalline H(2)O and CH(4) ice, as well as C(2)H(6) and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination. Conclusions. Model fits indicate that N(2) may be a significant component, along with a component that is bright at lambda > 3.3 mu m, which we suggest at this time could be amorphous H(2)O ice in tiny grains or thin grain coatings. Irradiated crystalline H(2)O could be the source of small-grained amorphous H(2)O ice. The albedo and composition of Quaoar, in particular the presence of N(2), if confirmed, make this TNO quite similar to Triton and Pluto

Ensemble Properties of Comets in the Sloan Digital Sky Survey

We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u,g,r,i,z) photometry is used to determine the comets' colors, sizes, surface brightness profiles, and rates of dust production in terms of the Af{\rho} formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(< H) \propto 10(0.49\pm0.05)H for H < 18, with evidence of a much shallower fit N(< H) \propto 10(0.19\pm0.03)H for the faint (14.5 < H < 18) comets. The resolved comets show an extremely narrow distribution of colors (0.57 \pm 0.05 in g - r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.Comment: 19 pages, 8 tables, 11 figures, to appear in Icaru