[en] Bench scale runs on concentration of intermediate level radioactive wastes, and incorporation of the concentrates in asphalt, are described. The feasibility of the process has been demonstrated, with a maximum incorporation of 60 percent of salts into the asphaltic matrix and a volume reduction factor of 10. (Author) 14 refs

[en] A characterization study was done to analyze how microstructural regions affect the mechanical properties, corrosion and fractography of the Heat Affected Zone (HAZ), weld bead and base metal for pipe naturally aged for 21 years at 30 degree centigrade. Results showed that microstructures exhibited damage and consequently decrease in properties, resulting in over-aged due to service. SEM analysis showed that base metal presented coarse ferrite grain. Tensile test indicated that microstructures showed discontinuous yield. Higher tensile strength was obtained for weld bead, which exhibited a lower impact energy in comparison to that of HAZ and base metal associated with brittle fracture by trans-granular cleavage. The degradation of properties was associated with the coarsening of nano-carbides observed through TEM images analysis, which was confirmed by SEM fractography of tensile and impact fracture surfaces. The weld bead reached the largest void density and highest susceptibility to corrosion in H₂S media when compared to those of the HAZ and base metal. (Author)

[en] The coastline of Veracruz is a unique environment due to the presence of extensive coraline systems and of natural oil seeps. Depending on the environmental parameters the coraline system are highly productive and diverse. Changes in these parameters by non-natural processes will cause damage or even the disappearance of these systems. Thus baseline studies in the zone are important in order to establish the natural concentrations of trace metals and the presence of petroleum hydrocarbons originated either from natural oil seeps or accidental spills. In the present paper the concentrations of nickel and vanadium in seawater and in sediments, as well as petroleum hydrocarbons in sediments are described in order to obtain base line information for the assessment of future man-induced alterations of the study area

[en] A full time-dependent kinetic study is presented for the main microscopic collisional and radiative processes underlying the optical flashes associated with an impulsive (τ = 5 μs) discharge in the form of a single sprite streamer passing through an air region of the mesosphere at three different altitudes (63, 68 and 78 km). The kinetic formalism developed includes the coupling of the rate equations of each of the different species considered (electrons, ions, atoms and molecules) with the Boltzmann transport equation so that, in this way, all the kinetics is self-consistent, although, in the present approach, the electrodynamics (no Poisson equation is considered) is not coupled. The chemical model set up for air plasmas includes more than 75 species and almost 500 reactions. In addition, a complete set of reactions (more than 110) has been considered to take into account the possible impact of including H₂O (humid chemistry) in the generated air plasmas. This study also considers the vibrational kinetics of N₂ and CO₂ and explicitly evaluates the optical emissions associated with a number of excited states of N₂, O₂, O in the visible, CO₂ in the infrared (IR) and ultraviolet (UV) emissions of sprite streamers due to the N₂ Lyman-Birge-Hopfield (LBH) and the NO-γ band systems. All the calculations are conducted for midnight conditions in mid-latitude regions (+38 deg. N) and 0 deg. longitude, using as initial values for the neutral species those provided by the latest version of the Whole Atmosphere Community Climate Model (WACCM). According to our calculations, the impact of 4 ppm of H₂O is only slightly visible in O₃^- at 68 and 78 km while it strongly affects the behaviour of the anion CO₄^- at all the altitudes investigated. The local enhancement of NO_x predicted by the present model varies with the altitude. At 68 km, the concentrations of NO and NO₂ increase by about one order of magnitude while that of NO₃ exhibits a remarkable growth of up to almost three orders of magnitude. The variation of the O₃ density predicted by the model in the sprite streamer head is negligible in all the altitudes investigated. The analysis of the time dependence of the electron distribution function (EDF) in the sprite plasma during the pulse reveals that the EDF transient is quite fast, reaching its 'steady' values during the pulse in less than 100 ns (much shorter than streamer head lifetimes). In addition, the calculated EDF during the pulse and in the afterglow is far from being Maxwellian, especially for energetic electrons (with ε > 30 eV). Finally, the evaluation of the mid-latitude nighttime electrical conductivity of air plasmas under the influence of a single sprite event reveals an increase of up to four orders of magnitude (at 68 km) above its measured background level of 10¹¹Ρcm^-1 at an altitude of ∼70 km. This sudden increase in the electrical conductivity lasts for 100 ms (at 68 km), being shorter (∼1 ms) and longer (1 s) at 63 km and 78 km, respectively. The total power delivered by the streamer head of a single sprite event has been estimated to be approximately 1677 W (at 78 km), 230 kW (at 68 km) and 78 MW (at 63 km).

No abstract available

[en] The RF coil arrays are an important part in Magnetic Resonance Imaging, since they are the main device for transmission and reception of the magnetic resonance signal. An RF coil array with a new configuration based on the Kepler's Lenten pretzel for the geocentric path of Mars is proposed in this work. The evenly distributed trajectories may serve as the basic configuration to form a coil array to adequately cover a region of interest for magnetic resonance experiments. The main goal is to investigate the electromagnetic properties of this coil array geometry to obtain an optimal design for its further construction. Hence, the electromagnetic properties of the coil array were numerical simulated using the finite element method and the quasi-static approach. Resulting simulations showed that there is an important concentration of magnetic field lines at the centre of the coil array. This is an advantage over other coil arrays where the magnetic field usually decreased at their geometrical centre. Both the electric and magnetic fields had also a very good uniformity. These characteristics made this coil design a good candidate for applications where the use of multi-coil technology is mandatory

[en] We study an opinion dynamics model that explores the competition between persuasion and compromise in a population of agents with nearest-neighbor interactions on a two-dimensional square lattice. Each agent can hold either a positive or a negative opinion orientation, and can have two levels of intensity—moderate and extremist. When two interacting agents have the same orientation they become extremists with persuasion probability p, while if they have opposite orientations they become moderate with compromise probability q. These updating rules lead to the formation of same-opinion domains with a coarsening dynamics that depends on the ratio r  =  p/q. The population initially evolves to a centralized state for small r, where domains are composed of moderate agents and coarsening is without surface tension, and to a bi-polarized state for large r, where domains are formed by extremist agents and coarsening is driven by curvature. Consensus in an extreme opinion is finally reached in a time that scales with the population size N and r as for small r and as for large r. Bi-polarization could be quite stable when the system falls into a striped state where agents organize into single-opinion horizontal, vertical or diagonal bands. An analysis of the stripe dynamics towards consensus allows us to obtain an approximate expression for τ, which shows that the exponent 1.64 is a result of the diffusion of the stripe interfaces combined with their roughness properties. (paper: interdisciplinary statistical mechanics)

[en] We study opinion formation in a population of leftists, centrists and rightist. In an interaction between neighbouring agents, a centrist and a leftist can become both centrists or leftists (and similarly for a centrist and a rightist), while leftists and rightists do not affect each other. The evolution is controlled by the initial density of centrists ρ₀. For any spatial dimension the system reaches a centrist consensus with probability ρ₀, while with probability 1 - ρ₀ the final state is either an extremist consensus, or a frozen population of leftists and rightists. In one dimension, we determine the opinion evolution by mapping the system onto a spin-1 Ising model with zero-temperature Glauber kinetics. The approach to the final state is governed by a t^-ψ long-time tail, with ψ → 2ρ₀/π as ρ₀ → 0. In the one-dimensional frozen state, the length distribution of single-opinion domains has an algebraic small-size tail x^-2(1-ψ) and the average domain length is L^2ψ, where L is the length of the system. (letter to the editor)

[en] We have used a kinetic model to investigate the influence of changing the pressure (0.1-0.8 Torr) and power (100-300 W) on the non-equilibrium plasma chemistry of RF (13.56 MHz) produced C₂H₂ (1%)/H₂/Ar plasmas of interest for the synthesis of nanodiamond thin films. We found that the concentrations of the species C₂(X¹SIGMA⁺_g), C₂(a³PI_u) and C₂H are not sensitive to variations in the power but they exhibit a significant increase when the pressure decreases at high argon content in the plasma. In addition, the concentrations of C₂H₂, CH₄ and CH₃ exhibit a slight (case of C₂H₂) or negligible (case of CH₃ and CH₄) power-dependence although they decrease (case of C₂H₂ and CH₄) or remain almost constant (case of CH₃) as the pressure decreases. A reasonable agreement is found when comparing the model predictions with available experimental results. These findings provide a basic understanding of the plasma chemistry of hydrocarbon/Ar-rich plasma environments and, at the same time, can be of interest to optimize the processing conditions of nanodiamond films from medium pressure RF hydrocarbon/Ar-rich plasmas

[en] In this work is estimated variance kerma function pixel values for the real response curve nonlinear digital image system, without resorting to any approximation to the behavior of the detector. This result is compared with that obtained for the linearized version of the response curve.