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[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 NOx 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).
[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 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 L2ψ, 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(a3PIu) 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.
[en] One of the suggestions in the new Protocol (February 2010) of the European Association of Nuclear Medicine Routine quality control recommendations for nuclear medicine instrumentation is to record the value cps / MBq obtained in carrying out this test to track sensitivity thus obtained. Ideally, this sensitivity should remain constant over time. At our institution this parameter has been registered since February 2009. In this paper we analyze data collected through December 2010 (23 months), relating the apparent loss of sensitivity downtime losses.