Core instability models of giant planet accretion II: forming planetary systems

We develop a simple model for computing planetary formation based on the core instability model for the gas accretion and the oligarchic growth regime for the accretion of the solid core. In this model several planets can form simultaneously in the disc, a fact that has important implications specially for the changes in the dynamic of the planetesimals and the growth of the cores since we consider the collision between them as a source of potential growth. The type I and II migration of the embryos and the migration of the planetesimals due to the interaction with the disc of gas are also taken into account. With this model we consider different initial conditions to generate a variety of planetary systems and analyse them statistically. We explore the effects of using different type I migration rates on the final number of planets formed per planetary system such as on the distribution of masses and semimajor axis of extrasolar planets, where we also analyse the implications of considering different gas accretion rates. A particularly interesting result is the generation of a larger population of habitable planets when the gas accretion rate and type I migration are slower.Comment: 4 figures and 1 table. Accepted for publication in MNRA

Iron oxide nanoparticles fabricated by electric explosion of wire: Focus on magnetic nanofluids

Nanoparticles of iron oxides (MNPs) were prepared using the electric explosion of wire technique (EEW). The main focus was on the fabrication of de-aggregated spherical nanoparticles with a narrow size distribution. According to XRD the major crystalline phase was magnetite with an average diameter of MNPs, depending on the fraction. Further separation of air-dry EEW nanoparticles was performed in aqueous suspensions. In order to provide the stability of magnetite suspension in water, we found the optimum concentration of the electrostatic stabilizer (sodium citrate and optimum pH level) based on zeta-potential measurements. The stable suspensions still contained a substantial fraction of aggregates which were disintegrated by the excessive ultrasound treatment. The separation of the large particles out of the suspension was performed by centrifuging. The structural features, magnetic properties and microwave absorption of MNPs and their aqueous solutions confirm that we were able to obtain an ensemble in which the magnetic contributions come from the spherical MNPs. The particle size distribution in fractionated samples was narrow and they showed a similar behaviour to that expected of the superparamagnetic ensemble. Maximum obtained concentration was as high as 5 % of magnetic material (by weight). Designed assembly of de-aggregated nanoparticles is an example of on-purpose developed magnetic nanofluid. Copyright © 2012 Author(s)

Preparation of alumina nanoparticle suspensions with narrow particle size distribution

Dynamic light scattering (DLS) was applied to the study of the process of the preparing deaggregated water suspensions of alumina nanopowders with specific surface areas of 20-140 m2/g. Nanopowders were prepared by the electric explosion of wire and laser evaporation and, according to electron microscopy (TEM), consisted of nonagglomerated spherical nanoparticles with lognormal size distribution. According to DLS, nonsedimenting water suspensions of alumina nanoparticles, stabilized by sodium citrate at a 5 mM concentration, contain substantial fraction of aggregates. The dynamics of the change in the mean average size of aggregates under exhaustive ultrasound treatment of suspensions with 10 g/l concentration for 1.5-4 h by two types of ultrasonic processors was studied. It was shown that the mean average size of aggregates exponentially diminishes by 1.5-2 times and the fraction of individual particles in suspension enlarges from 45 to 85%. Sequentially centrifuging the suspension at 18000 g separates the remaining aggregates and results in suspensions of individual alumina nanoparticles. Particle size distributions in these suspensions obtained by TEM and DLS are the same within experimental error. © 2013 Pleiades Publishing, Ltd

Carbon coated Nickel Nanoparticles in Polyacrylamide Ferrogels: Interaction with Polymeric Network and Impact on Swelling

Polyacrylamide ferrogels with embedded magnetic nanoparticles of metallic nickel (Ni) and nanoparticles of nickel coated with a carbon shell (Ni@C) were synthesized by radical polymerization in water. The effect of the carbon shell on the interaction of Ni and Ni@C nanoparticles with polyacrylamide matrix and on swelling ratio of the ferrogels has been studied. The deposition of carbon on the surface of Ni nanoparticles worsens their interaction with polyacrylamide but at the same time elevates the water uptake by ferrogels

Electomagnetic absorption of composites based on epoxy resin and metallic iron nanoparticles

The heat losses originated from the electro-magnetic absorption in magnetic epoxy-based composites with embedded metallic iron nanoparicles were studied by Calvet microcalorimetry. Iron magnetic nanoparticles (MNPs) were synthesized by electrical explosion of wire (EEW) method; they were non-agglomerated, spherical in shape and had a weight average diameter 85 nm. Composites based on the cured epoxy-dian resin contained MNPs in weight content varying from 10% up to 70%. To study the heat loss in alterating magnetic field commercial Calvet microcalorimeter was equiped by two coils in the serial connection placed in the calorimeter cells; one of the coils contained a sample of composite the other was a reference. The electromagnetic adsorption was studied in the alternating magnetic field up to 1700 A/m in 67-214 kHz frequency range. The measured values of the specific power losses revealed linear dependence on iron MNPs content in composite and non-linear increasing function of the field frequency. © 2018 The Authors, published by EDP Sciences.This work is supported in part by the project for basic research of UD RAS. The assistance of Shchipanova T. A. in the measurements of hysteresis loops for composites is appreciated