1,195 research outputs found
Field-guided proton acceleration at reconnecting X-points in flares
An explicitly energy-conserving full orbit code CUEBIT, developed originally
to describe energetic particle effects in laboratory fusion experiments, has
been applied to the problem of proton acceleration in solar flares. The model
fields are obtained from solutions of the linearised MHD equations for
reconnecting modes at an X-type neutral point, with the additional ingredient
of a longitudinal magnetic field component. To accelerate protons to the
highest observed energies on flare timescales, it is necessary to invoke
anomalous resistivity in the MHD solution. It is shown that the addition of a
longitudinal field component greatly increases the efficiency of ion
acceleration, essentially because it greatly reduces the magnitude of drift
motions away from the vicinity of the X-point, where the accelerating component
of the electric field is largest. Using plasma parameters consistent with flare
observations, we obtain proton distributions extending up to gamma-ray-emitting
energies (>1MeV). In some cases the energy distributions exhibit a bump-on-tail
in the MeV range. In general, the shape of the distribution is sensitive to the
model parameters.Comment: 14 pages, 4 figures, accepted for publication in Solar Physic
Propagating EUV disturbances in the solar corona : two-wavelength observations
Quasi-periodic EUV disturbances simultaneously observed in 171 Ã… and 195 Ã… TRACE bandpasses propagating outwardly in a fan-like magnetic structure of a coronal active region are analysed. Time series of disturbances observed in the different bandpasses have a relatively high correlation coefficient (up to about 0.7). The correlation has a tendency to decrease with distance along the structure: this is consistent with an interpretation of the disturbances in terms of parallel-propagating slow magnetoacoustic waves. The wavelet analysis does not show a significant difference between waves observed in different bandpasses. Periodic patterns of two distinct periods: 2-3 min and 5-8 min are detected in both bandpasses, existing simultaneously and at the same distance along the loop, suggesting the nonlinear generation of the second harmonics
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
Collisional damping rates for plasma waves
The distinction between the plasma dynamics dominated by collisional
transport versus collective processes has never been rigorously addressed until
recently. A recent paper [Yoon et al., Phys. Rev. E 93, 033203 (2016)]
formulates for the first time, a unified kinetic theory in which collective
processes and collisional dynamics are systematically incorporated from first
principles. One of the outcomes of such a formalism is the rigorous derivation
of collisional damping rates for Langmuir and ion-acoustic waves, which can be
contrasted to the heuristic customary approach. However, the results are given
only in formal mathematical expressions. The present Brief Communication
numerically evaluates the rigorous collisional damping rates by considering the
case of plasma particles with Maxwellian velocity distribution function so as
to assess the consequence of the rigorous formalism in a quantitative manner.
Comparison with the heuristic ("Spitzer") formula shows that the accurate
damping rates are much lower in magnitude than the conventional expression,
which implies that the traditional approach over-estimates the importance of
attenuation of plasma waves by collisional relaxation process. Such a finding
may have a wide applicability ranging from laboratory to space and
astrophysical plasmas.Comment: 5 pages, 2 figures; Published in Physics of Plasmas, volume/Issue
23/6. Publisher: AIP Publishing LLC. Date: Jun 1, 2016. URL:
http://aip.scitation.org/doi/10.1063/1.4953802 Rights managed by AIP
Publishing LL
Solar Flares as Cascades of Reconnecting Magnetic Loops
A model for the solar coronal magnetic field is proposed where multiple
directed loops evolve in space and time. Loops injected at small scales are
anchored by footpoints of opposite polarity moving randomly on a surface.
Nearby footpoints of the same polarity aggregate, and loops can reconnect when
they collide. This may trigger a cascade of further reconnection, representing
a solar flare. Numerical simulations show that a power law distribution of
flare energies emerges, associated with a scale free network of loops,
indicating self-organized criticality.Comment: 4 pages, 4 figures, To be published in Phys. Rev. Let
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Bio-Based Formulations for Sustainable Applications in Agri-Food-Pharma
Currently, there is a strong enduring interest towards obtaining high-value, sustainable bio-based bioactive compounds from natural resources, as there is great demand for these compounds in various market sectors such as agriculture, food, pharma, cosmeceuticals, and others. This demand has encouraged researchers to isolate, identify and characterize novel natural bioactive compounds with potential therapeutic and commercial values with industrial importance [1]. These bioactive compounds are generally secondary metabolites (synthesized via plant biosynthetic pathways) and include polyphenols, carotenoids, flavonoids, sterols, dietary fiber, essential vitamins, coenzyme Q, phytosterols, glucosinolates and others with potential beneficial roles as nutraceuticals, surfactants and bio-stimulants. Understanding the molecular characteristics, physicochemical properties, biological activity, and stability of these bioactives under different conditions is vital for their commercial exploitation. The efficacy of these bioactives can often be improved by encapsulating them in nanobased-formulations designed for application in the agriculture, food, pharmaceutical industries. These delivery systems can be designed to increase the dispersibility, stability, bioavailability, and bioactivity imparted by the bioactives. Moreover, they may be useful for minimizing undesirable side-effects, facilitating targeted delivery to certain cells, and enhancing the shelf life of food products
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