7,666 research outputs found
Various measures to achieve the EU goal for the use of bioenergy with special focus on field energy. Challenges for agricultural policy
The growing interest in biomass and energy produced from this is mainly considered a positive thing in terms of current agricultural production. Increased use of renewable resources as biomass gives a good opportunity to agriculture to promote its positive environmental functions and to make its contribution to the work to prevent climate change
Three-wave interactions of dispersive plasma waves propagating parallel to the magnetic field
Three-wave interactions of plasma waves propagating parallel to the mean
magnetic field at frequencies below the electron cyclotron frequency are
considered. We consider Alfv\'en--ion-cyclotron waves,
fast-magnetosonic--whistler waves, and ion-sound waves. Especially the weakly
turbulent low-beta plasmas like the solar corona are studied, using the
cold-plasma dispersion relation for the transverse waves and the
fluid-description of the warm plasma for the longitudinal waves. We analyse the
resonance conditions for the wave frequencies and wavenumbers , and
the interaction rates of the waves for all possible combinations of the three
wave modes, and list those reactions that are not forbidden.Comment: accepted for publication in Advanced Science Letter
Utilitarian and moralistic farmers take equally good care of animal welfare in Finland
A study of Finnish farmers' attitudes towards production animal welfare revealed that a variety of attitudes and management practices can lead to equally good result regarding animal health, productivity and welfare. Organic farmers differed from conventional farmers in providing animals better chances for a pleasant life. The also perceived they could improve animal welfare more than other farmers
Evolution of plasma turbulence excited with particle beams
Particles ejected from the Sun that stream through the surrounding plasma of
the solar wind are causing instabilities. These generate wavemodes in a certain
frequency range especially within shock regions, where particles are
accelerated. The aim of this paper is to investigate of amplified Alfvenic
wavemodes in driven incompressible magnetohydrodynamic turbulence. Results of
different heliospheric scenarios from isotropic and anisotropic plasmas, as
well as turbulence near the critical balance are shown. The energy transport of
the amplified wavemode is governed by the mechanisms of diffusion, convection
and dissipation of energy in wavenumber space. The strength of these effects
varies with energy and wavenumber of the mode in question. Two-dimensional
energy spectra of spherical k-space integration that permit detailed insight
into the parallel and perpendicular development are presented. The evolution of
energy injected through driving shows a strong energy transfer to perpendicular
wavemodes. The main process at parallel wavemodes is the dissipation of energy
in wavenumber space. The generation of higher harmonics along the parallel
wavenumber axis is observed. We find evidence for a critical balance in our
simulations.Comment: Accepted for publication in A&
Stochastic Acceleration in Relativistic Parallel Shocks
(abridged) We present results of test-particle simulations on both the first
and the second order Fermi acceleration at relativistic parallel shock waves.
We consider two scenarios for particle injection: (i) particles injected at the
shock front, then accelerated at the shock by the first order mechanism and
subsequently by the stochastic process in the downstream region; and (ii)
particles injected uniformly throughout the downstream region to the stochastic
process. We show that regardless of the injection scenario, depending on the
magnetic field strength, plasma composition, and the employed turbulence model,
the stochastic mechanism can have considerable effects on the particle spectrum
on temporal and spatial scales too short to be resolved in extragalactic jets.
Stochastic acceleration is shown to be able to produce spectra that are
significantly flatter than the limiting case of particle energy spectral index
-1 of the first order mechanism. Our study also reveals a possibility of
re-acceleration of the stochastically accelerated spectrum at the shock, as
particles at high energies become more and more mobile as their mean free path
increases with energy. Our findings suggest that the role of the second order
mechanism in the turbulent downstream of a relativistic shock with respect to
the first order mechanism at the shock front has been underestimated in the
past, and that the second order mechanism may have significant effects on the
form of the particle spectra and its evolution.Comment: 14 pages, 11 figures (9 black/white and 2 color postscripts). To be
published in the ApJ (accepted 6 Nov 2004
Iron-rich solar particle events measured by SOHO/ERNE during two solar cycles
We study the differences in the heavy ion composition of solar energetic
particle (SEP) events between solar cycles 23 and 24. We have surveyed the
SOHO/ERNE heavy ion data from the beginning of solar cycle 23 until the end of
June 2015, that is, well into the declining phase of cycle 24. We used this
long observation period to study the properties of heavy ions (from C to Fe)
and to compare the two solar cycles in this respect. We surveyed the data for
SEP events with enhancements in the Fe/C and Fe/O intensity ratios in the
energy range 5-15 MeV per nucleon, and associated the events with solar flare
and coronal mass ejections (CME) when possible. We studied the properties of
heavy ions in these events and compared the average relative abundances of
heavy ions between the two solar cycles. We found that fewer days had C and O
intensities higher than ~10
cmsrs(MeVn) during solar cycle 24 than
during cycle 23. For Fe this difference was clear even at lower intensities. We
also found that fewer days had Fe/(C+O) > 0.183 during cycle 24. We identified
86 SEP events with at least one Fe-rich day, 65 of which occurred during cycle
23 and only 21 during cycle 24. We found that impulsive events have been almost
completely absent during cycle 24. Mean abundances of heavy ions in the events
were found to be significantly lower during cycle 24 than in cycle 23. Our
results reflect the reduced solar activity in cycle 24 and indicate lower
efficiency of particle acceleration processes for both gradual and impulsive
SEP events in cycle 24.Comment: 14 pages, 9 figures and 3 tables. To be published in A&
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