On Plane Waves in Diluted Relativistic Cold Plasmas

We briefly report on some exact results (Fiore in J. Phys. A, Math. Theor. 47:225501, 2014) regarding plane waves in a relativistic cold plasma. If the plasma, initially at rest, is reached by a transverse plane electromagnetic travelling-wave, then its motion has a very simple dependence on this wave in the limit of zero density, otherwise can be determined by an iterative procedure whose accuracy decreases with time or the plasma density. Thus one can describe in particular the impact of a very intense and short laser pulse onto a plasma and determine conditions for the slingshot effect (Fiore et al. in arXiv:1309.1400, 2014) to occur. The motion in vacuum of a charged test particle subject to a wave of the same kind is also determined, for any initial velocity.     

One-pot synthesis and characterization of size-controlled bimagnetic FePt-iron oxide heterodimer nanocrystals

A one-pot, two-step colloidal strategy to prepare bimagnetic hybrid nanocrystals (HNCs), comprising size-tuned fcc FePt and inverse spinel cubic iron oxide domains epitaxially arranged in a heterodimer configuration, is described. The HNCs have been synthesized in a unique surfactant environment by temperature-driven sequential reactions, involving the homogeneous nucleation of FePt seeds and the subsequent heterogeneous growth of iron oxide. This self-regulated mechanism offers high versatility in the control of the geometric features of the resulting heterostructures, circumventing the use of more elaborate seeded growth techniques. It has been found that, as a consequence of the exchange coupling between the two materials, the HNCs exhibit tunable single-phase-like magnetic behavior, distinct from that of their individual components. In addition, the potential of the heterodimers as effective contrast agents for magnetic resonance imaging techniques has been examined.     

Space-charge effects in the current-filamentation or Weibel instability

We consider how an unmagnetized plasma responds to an incoming flux of energetic electrons. We assume a return current is present and allow for the incoming electrons to have a different transverse temperature than the return current. To analyze this configuration we present a nonrelativistic theory of the current-filamentation or Weibel instability for rigorously current-neutral and nonseparable distribution functions, f(0)(p(x), p(y), p(z)) is not equal to f(x)(p(x))f(y)(p(y))f(z)(p(z)). We find that such distribution functions lead to lower growth rates because of space-charge forces that arise when the forward-going electrons pinch to a lesser degree than the colder, backward-flowing electrons. We verify the growth rate, range of unstable wave numbers, and the formation of the density filaments using particle-in-cell simulations.     

Canonical and microcanonical Monte Carlo simulations of lattice-gas mixtures

We propose strict canonical and microcanonical Monte Carlo algorithms for an arbitrary lattice-gas binary mixture. We deduce formulas that allow us to obtain field quantities over the ensembles in which their conjugate extensive quantities are conserved. As an example, we have considered a lattice-gas mixture that is equivalent to the spin-1 Blume-Emery-Griffiths model [Phys. Rev. A 4, 1071 (1971)]. For a finite system and near a phase coexistence, the field as a function of its extensive conjugate shows a loop that disappears in the thermodynamic limit giving rise to the usual tie line. The first-order phase transition was determined by the use of three criteria.     

Thermal analysis, fragility and viscosity of Au-based metallic glasses

Metallic glasses based on Au of composition Au₄₉Cu_26.9Ag_5.5Pd_2.3Si_16.3 and (Au₄₉Cu_26.9Ag_5.5Pd_2.3Si_16.3)₉₉X₁ where X = Ti and In, have been produced and characterized in ribbon form. They show a glass transition and a rather wide undercooled liquid region before crystallisation.The fragility index (m) of the alloys was investigated with two methods involving differential scanning calorimetry (DSC) measurements. In one method the glass transition temperature was determined at different scanning rates in the range 0.3-100 °C/min and its trend fitted to give m. In the other m was obtained from the temperature span of the glass transition range at the scanning rate of 20 °C/min. Implications for viscosity in the undercooled liquid are derived and thoroughly discussed ending with a VFT (Vogel-Fulcher-Tammann) expression for it.     

Mercury speciation in the colloidal fraction of a soil polluted by a chlor‐alkali plant: a case study in the South of Italy

Mercury (Hg) speciation in different size fractions of a soil sample collected near an industrial area located in the South of Italy, which had been polluted by the dumping of Hg‐containing wastes from a chlor‐alkali plant, was investigated by XANES spectroscopy. In particular, a special procedure has been developed to study the soil colloidal fraction, both for sample preparation and for XANES data collection. In this soil, Hg was speciated in quite insoluble inorganic forms such as cinnabar (α‐HgS), metacinnabar (β‐HgS), corderoite (Hg₃S₂Cl₂), and some amorphous Hg, S and Cl‐containing species, all derived from the land‐disposal of K106 Hg‐containing wastes. The contribution of the above‐mentioned chemical forms to Hg speciation changed as a function of particle size. For the fraction <2 mm the speciation was: amorphous Hg–S–Cl (34%) > corderoite (26%) > cinnabar (20%) = metacinnabar (20%); for the fraction <2 µm: amorphous Hg–S–Cl (40%) > metacinnabar (24%) > corderoite (20%) > cinnabar (16%); and for the fraction 430–650 nm, where most of the colloidal Hg was concentrated: amorphous Hg–S–Cl (56%) > metacinnabar (33%) > corderoite (6%) > cinnabar (5%). From these data it emerged that, even if Hg was speciated in quite insoluble forms, the colloidal fraction, which is the most mobile and thus the most dangerous, was enriched in relatively more soluble species (i.e. amorphous Hg–S–Cl and metacinnabar), as compared with cinnabar. This aspect should be seriously taken into account when planning environmental risk assessment, since the small particle size in which Hg is concentrated and the changing speciation passing from millimetre to nanometre size could turn apparently safe conditions into more hazardous ones.