2,052 research outputs found
Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence
Using test-particle simulations, we investigate the temporal dependence of
the two-point velocity correlation function for charged particles scattering in
a time-independent spatially fluctuating magnetic field derived from a
three-dimensional isotropic turbulence power spectrum. Such a correlation
function allowed us to compute the spatial coefficients of diffusion both
parallel and perpendicular to the average magnetic field. Our simulations
confirm the dependence of the perpendicular diffusion coefficient on turbulence
energy density and particle energy predicted previously by a model for
early-time charged particle transport. Using the computed diffusion
coefficients, we exploit the particle velocity autocorrelation to investigate
the time-scale over which the particles "decorrelate" from the solution to the
unperturbed equation of motion. Decorrelation time-scales are evaluated for
parallel and perpendicular motions, including the drift of the particles from
the local magnetic field line. The regimes of strong and weak magnetic
turbulence are compared for various values of the ratio of the particle
gyroradius to the correlation length of the magnetic turbulence. Our simulation
parameters can be applied to energetic particles in the interplanetary space,
cosmic rays at the supernova shocks, and cosmic-rays transport in the
intergalactic medium.Comment: 10 pages, 11 figures, The Astrophyical Journal in pres
Particle acceleration by collisionless shocks containing large-scale magnetic-field variations
Diffusive shock acceleration at collisionless shocks is thought to be the
source of many of the energetic particles observed in space. Large-scale
spatial variations of the magnetic field has been shown to be important in
understanding observations. The effects are complex, so here we consider a
simple, illustrative model. Here, we solve numerically the Parker transport
equation for a shock in the presence of large-scale sinusoidal magnetic-field
variations. We demonstrate that the familiar planar-shock results can be
significantly altered as a consequence of large-scale, meandering magnetic
lines of force. Because perpendicular diffusion coefficient is
generally much smaller than parallel diffusion coefficient ,
the energetic charged particles are trapped and preferentially accelerated
along the shock front in the regions where the connection points of magnetic
field lines intersecting the shock surface converge, and thus create the "hot
spots" of the accelerated particles. For the regions where the connection
points separate from each other, the acceleration to high energies will be
suppressed. Further, the particles diffuse away from the "hot spot" regions and
modify the spectra of downstream particle distribution. These features are
qualitatively similar to the recent Voyager's observation in the Heliosheath.
These results are potentially important for particle acceleration at shocks
propagating in turbulent magnetized plasmas as well as those which contain
large-scale nonplanar structures. Examples include anomalous cosmic rays
accelerated by the solar wind termination shock, energetic particles observed
in propagating heliospheric shocks, and galactic cosmic rays accelerated by
supernova blast waves, etc.Comment: accepted to Ap
Fullerene-containing Polymers
In the present chapter, the different C60-based polymers have been classified according to structural parameters and the different synthetic strategies to prepare them have been highlighted. Two new families have been added, namely fullerene\u2013nanotubes hybrid and DNA\u2013fullerene hybrid, due to the nondiscrete nature of the corresponding members. Finally, fullerene-containing polymers\u2019 most promising applications have been discussed, mainly focusing on nonlinear optics, DNA-cleaving and photovoltaic properties
Reverse electrodialysis – Multi effect distillation heat engine fed by lithium chloride solutions
Salinity Gradient Heat Engines (SG-HEs) have been proposed as a promising technology for converting low-temperature heat into electricity. The SG-HE includes two different processes: (i) a salinity gradient process where the salinity gradient between two solutions is converted into electricity and (ii) a thermal regeneration process where low-grade heat (T<100°C) is used to re-establish the original salinity gradient of the two streams. Among the proposed working solutions, aqueous solution of lithium chloride has been identified as one of the most promising thanks to its remarkable solubility and activity. In this work, a process model to study the performance of a SG-HE constituted by a Reverse ElectroDialysis (RED) unit coupled with a Multi Effect Distillation (MED) unit fed with lithium chloride solution is presented. The influence of the concentration of the inlet solution in the RED unit and the temperature difference in the evaporators of the MED unit on the performance were evaluated by considering ideal membranes. Furthermore, the impact of membrane permselectivity and resistance on the system performance was evaluated. Results showed promising system efficiencies, making this technology attractive for conversion of low-grade heat (<100°C) into electricity, but membrane properties should be enhanced
Vortical amplification of magnetic field at inward shock of supernova remnant Cassiopeia A
We present an interpretation of the time variability of the -ray flux
recently reported from a multi-epoch campaign of years observations of the
supernova remnant Cassiopeia A by {\it Chandra}. We show for the first time
quantitatively that the keV non-thermal flux increase up to
traces the growth of the magnetic field due to vortical amplification mechanism
at a reflection inward shock colliding with inner overdensities. The fast
synchrotron cooling as compared with shock-acceleration time scale
qualitatively supports the flux decrease.Comment: 5 pages, 2 figures, PRL in pres
Evaluation of the economic and environmental performance of low-temperature heat to power conversion using a reverse electrodialysis - Multi-effect distillation system
In the examined heat engine, reverse electrodialysis (RED) is used to generate electricity from the salinity difference between two artificial solutions. The salinity gradient is restored through a multi-effect distillation system (MED) powered by low-temperature waste heat at 100 ◦C. The current work presents the first comprehensive economic and environmental analysis of this advanced concept, when varying the number of MED effects, the system sizing, the salt of the solutions, and other key parameters. The levelized cost of electricity (LCOE) has been calculated, showing that competitive solutions can be reached only when the system is at least medium to large scale. The lowest LCOE, at about 0.03 €/kWh, is achieved using potassium acetate salt and six MED effects while reheating the solutions. A similar analysis has been conducted when using the system in energy storage mode, where the two regenerated solutions are stored in reservoir tanks and the RED is operating for a few hours per day, supplying valuable peak power, resulting in a LCOE just below 0.10 €/kWh. A life-cycle assessment has been also carried out, showing that the case with the lowest environmental impact is the same as the one with the most attractive economic performance. Results indicate that the material manufacturing has the main impact; primarily the metallic parts of the MED. Overall, this study highlights the development efforts required in terms of both membrane performance and cost reduction, in order to make this technology cost effective in the future
Morphological variation of the newly confirmed population of the javelin sand boa, Eryx jaculus (Linnaeus, 1758) (Serpentes, erycidae) in Sicily, Italy
The presence of the Javelin sand boa in Sicily has recently been confirmed. Here the morphological characters and sexual dimorphism of the Sicilian population of Eryx jaculus are presented. Seven meristic and six metric characters in 96 specimens from Sicily were examined. The results show that tail length, snout-vent length, the distance between nostrils and the number of ventral and subcaudal scales are different between sexes. The characters found in the Sicilian population of the Javelin sand boa resemble those of the African population (ssp. jaculus) rather than the Eurasian population (ssp. turcicus), but biomolecular studies are necessary to understand its taxonomic identity
Diffusion of energetic particles in turbulent MHD plasmas
In this paper we investigate the transport of energetic particles in
turbulent plasmas. A numerical approach is used to simulate the effect of the
background plasma on the motion of energetic protons. The background plasma is
in a dynamically turbulent state found from numerical MHD simulations, where we
use parameters typical for the heliosphere. The implications for the transport
parameters (i.e. pitch-angle diffusion coefficients and mean free path) are
calculated and deviations from the quasi-linear theory are discussed.Comment: Accepted for publication in Ap
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