Influence of addition order and contact time on thorium(IV) retention by hematite in the presence of humic acids

International audienceThe influence of addition order and contact time in the system hematite (alpha-Fe2O3)-humic acid (HA)-thorium(IV) (Th(IV)) was studied in batch experiments. Th(IV) is considered here as a chemical analogue of other actinides (IV). The sorption isotherms were acquired varying pH in the range 2-10 and HA concentration in the range 1-100 mg/L. As already observed by numerous authors, Th(IV) retention was hindered when HA and hematite were equilibrated beforehand during 24 h. As it has been observed in a previous study, this effect was drastic when the ratio between humic and surface (iron oxide) sites exceeds a critical value. However, when HA was added after a 24-h equilibration of the hematite-Th(IV) system, Th(IV) was barely desorbed from the iron oxide surface. Furthermore, no drastic effect of the ratio between humic and surface sites could be evidenced, as the increase of HA concentration only results in a slight monotonic decrease in Th(IV) retention. Increasing contact time between components of the systems only indicated slight Th(IV) retention variation. This was interpreted as a consequence of slow kinetic controls of both the Th(IV)-HA complexation and HA-hematite sorption

CCD photometric search for peculiar stars in open clusters VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

Context. We continue our survey of magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open cluster ages and metallicities can help for finding a correlation between these parameters and the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Methods. The intermediate band Δa photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the centre with the adjacent regions with bandwidths of 110 A to 230 A. It is capable of detecting magnetic CP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λBootis and classical Be/shell stars can be successfully investigated. In addition, it allows the age, reddening, and distance modulus to be determined with appropriate accuracy by fitting isochrones. Results. From the 1677 observed members of the eight open clusters, one Ae and twenty-five CP2 stars were identified. Furthermore nineteen deviating stars are designated as questionable for several reasons. The estimated age, reddening, and distance for the programme clusters were compared with published values of the literature and discussed in this context. Conclusions. The current paper shows that CP2 stars are continuously present in very young (7 Myr) to intermediate age (500 Myr) open clusters at distances greater than 2 kpc from the Sun. © ESO 2007.Fil: Netopil, M.. Universidad de Viena; AustriaFil: Paunzen, E.. Universidad de Viena; AustriaFil: Maitzen, H.M.. Universidad de Viena; AustriaFil: Pintado, Olga Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Claret, A.. Instituto de Astrofísica de Andalucía - Csic;Fil: Miranda, L.F.. Instituto de Astrofísica de Andalucía - Csic;Fil: Hiev, I.Kh.. National Astronomical Observatory Rozhen; BulgariaFil: Casanova, V.. Instituto de Astrofísica de Andalucía - Csic

On the study of Th(IV)-humic acid interactions by competition sorption studies with silica and determination of global interaction constants

http://www.radiochimacta.deInternational audienceThe influence of humic acids (HA) on the retention of thorium (IV) onto the surface of silica colloids is investigated. Thorium is considered as an analogue of tetravalent actinides (U, Np, Pu), except for the fact that it has no f electrons. Silica (SiO2) is chosen as a model surface because it is a component of many minerals and because of its weak HA sorption properties. Retention experiments are performed by batch procedure at constant ionic strength (I = 0.1M NaClO4), at various pH (2 to 9) and HA concentrations (1–100 mg/L). The sorption of Th(IV) onto colloidal amorphous silica is characterised using a surface complexation model. The ternary system (i.e. HA-Th-Silica) clearly shows the influence of HA on Th(IV) retention. This can lead to a strong reduction of the amount of Th(IV) sorbed onto silica in the presence of HA compared to silica colloids without HA, due to a predominant part of thorium present in solution as humic complexes. In a pH range where no organic coating onto silica occurs, there is a competitive reaction between Th(IV) sorption onto the silica surface and onto HA reactive functional groups. In this case, Schubert's method is applied to obtain a global interaction constant for the Th(IV)-HA system. The large interaction constant values indicate a strong affinity of HA for Th(IV)

Spanning avalanches in the three-dimensional Gaussian Random Field Ising Model with metastable dynamics: field dependence and geometrical properties

Spanning avalanches in the 3D Gaussian Random Field Ising Model (3D-GRFIM) with metastable dynamics at T=0 have been studied. Statistical analysis of the field values for which avalanches occur has enabled a Finite-Size Scaling (FSS) study of the avalanche density to be performed. Furthermore, direct measurement of the geometrical properties of the avalanches has confirmed an earlier hypothesis that several kinds of spanning avalanches with two different fractal dimensions coexist at the critical point. We finally compare the phase diagram of the 3D-GRFIM with metastable dynamics with the same model in equilibrium at T=0.Comment: 16 pages, 17 figure

The AMIGA sample of isolated galaxies - II. Morphological refinement

We present a complete POSS II-based refinement of the optical morphologies for galaxies in the Karatchenseva's Catalog of Isolated Galaxies that forms the basis of the AMIGA project. Comparison with independent classifications made for an SDSS overlap sample of more than 200 galaxies confirms the reliability of the early vs. late-type discrimination and the accuracy of spiral subtypes within DeltaT = 1-2. CCD images taken at the OSN were also used to solve ambiguities. 193 galaxies are flagged for the presence of nearby companions or signs of distortion likely due to interaction. This most isolated sample of galaxies in the local Universe is dominated by 2 populations: 1) 82% spirals (Sa-Sd) with the bulk being luminous systems with small bulges (63% between types Sb-Sc) and 2) a significant population of early-type E-S0 galaxies (14%). Most of the types later than Sd are low luminosity galaxies concentrated in the local supercluster where isolation is difficult to evaluate. The late-type spiral majority of the sample spans a luminosity range M_B-corr = -18 to -22 mag. Few of the E/S0 population are more luminous than -21.0 marking an absence of, an often sought, super L* merger (eg fossil elliptical) population. The rarity of high luminosity systems results in a fainter derived M* for this population compared to the spiral optical luminosity function (OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending how the sample is defined. This marks the AMIGA sample as almost unique among samples that compare early and late-type OLFs separately. In other samples, which always involve galaxies in higher density environments, M*(E/S0) is almost always 0.3-0.5 mag brighter than M*(S), presumably reflecting a stronger correlation between M* and environmental density for early-type galaxies.Comment: A&A accepted, 13 pages, 9 figures, 8 tables. Higher resolution Fig. 1 and full tables are available on the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) website at http://www.iaa.es/AMIGA.htm

Transit analysis of the CoRoT-5, CoRoT-8, CoRoT-12, CoRoT-18, CoRoT-20, and CoRoT-27 systems with combined ground- and space-based photometry

We have initiated a dedicated project to follow-up with ground-based photometry the transiting planets discovered by CoRoT in order to refine the orbital elements, constrain their physical parameters and search for additional bodies in the system. From 2012 September to 2016 December we carried out 16 transit observations of six CoRoT planets (CoRoT-5b, CoRoT-8b, CoRoT-12b, CoRoT-18b, CoRoT-20b, and CoRoT-27b) at three observatories located in Germany and Spain. These observations took place between 5 and 9 yr after the planet's discovery, which has allowed us to place stringent constraints on the planetary ephemeris. In five cases we obtained light curves with a deviation of the mid-transit time of up to ~115min from the predictions. We refined the ephemeris in all these cases and reduced the uncertainties of the orbital periods by factors between 1.2 and 33. In most cases our determined physical properties for individual systems are in agreement with values reported in previous studies. In one case, CoRoT-27b, we could not detect any transit event in the predicted transit window.Comment: 17 pages, 23 figures, 15 tables, accepted by MNRA

Stability of casein micelles cross-linked with genipin: a physicochemical study as a function of pH

Chemical or enzymatic cross-linking of casein micelles (CMs) increases their stability against dissociating agents. In this paper, a comparative study of stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a function of pH is described. Stability to temperature and ethanol were investigated in the pH range 2.0-7.0. The size and the charge ($\zeta$-potential) of the particles were determined by dynamic light scattering. Native CMs precipitated below pH 5.5, CMs-GP precipitated from pH 3.5 to 4.5, whereas no precipitation was observed at pH 2.0-3.0 or pH 4.5-7.0. The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability against heat and ethanol was observed for CMs-GP at pH 2, where visible coagulation was determined only after 800 s at 140 $^\circ$C or 87.5% (v/v) of ethanol. These results confirmed the hypothesis that cross-linking by GP increased the stability of CMs.Comment: 5 pages, 2 figures, International Dairy Journal, 201

Discriminación de bosques de Araucaria araucana en el Parque Nacional Conguillío, centro-sur de Chile, mediante datos Landsat TM

Martin, JS (San Martin, Jose). Univ Talca, Inst Biol Vegetal & Biotecnol, Talca, ChileAraucaria forests (Araucaria araucana) have a tremendous ecological relevance; however, the information concerning their spatial distribution is still insufficient. They have only been classified according to small management scales, using satellite photos and images processed through conventional methods. The present study had as its objective to discriminate and characterize types of A. araucana forests in the Conguillio National Park, located in the Southern-Center Chile, through data derived from the Landsat-5 TM satellite and geographic information systems. The normalized difference vegetation index (NDVI) was satisfactorily related with variables corresponding to crown coverage and the diameter at breast height; thus, these index values were incorporated to the classification process. Using the digital elevation model and the NDVI, the effect provoked by the shadow was minimized. Seven types of forests, between dense and semi-dense-open, were discriminated in accordance with the accompanying species. The global reliability of the classification was 83.8 %. The greatest reliability for the producer was for the medium crown density forest of A. araucana - N. dombeyi (B1) (87.5 %); and for the consumer, for the high crown density forests of A. araucana - N. dombeyi (B1) and also for those of medium density (B2) (93 %). It is concluded that incorporating NDVI values and data derived from the digital elevation model to the satellite classification process, it is possible to discriminate araucaria forests with satisfactory reliability in areas of rough relief, which is very useful information for the management of these forestry ecosystems

Vigilância na Gravidez: Estudo hospitalar 2003

O presente estudo pretende avaliar a repercussão do adequado seguimento da gravidez relativamente à sua evolução e à morbi-mortalidade do recém-nascid