1,502 research outputs found
Accelerated particle beams in a 3D simulation of the quiet Sun
Observational and theoretical evidence suggest that beams of accelerated
particles are produced in flaring events of all sizes in the solar atmosphere,
from X-class flares to nanoflares. Current models of these types of particles
in flaring loops assume an isolated 1D atmosphere. A more realistic environment
for modelling accelerated particles can be provided by 3D radiative
magnetohydrodynamics codes. Here, we present a simple model for particle
acceleration and propagation in the context of a 3D simulation of the quiet
solar atmosphere, spanning from the convection zone to the corona. We then
examine the additional transport of energy introduced by the particle beams.
The locations of particle acceleration associated with magnetic reconnection
were identified by detecting changes in magnetic topology. At each location,
the parameters of the accelerated particle distribution were estimated from
local conditions. The particle distributions were then propagated along the
magnetic field, and the energy deposition due to Coulomb collisions with the
ambient plasma was computed. We find that particle beams originate in extended
acceleration regions that are distributed across the corona. Upon reaching the
transition region, they converge and produce strands of intense heating that
penetrate the chromosphere. Within these strands, beam heating consistently
dominates conductive heating below the bottom of the transition region. This
indicates that particle beams qualitatively alter the energy transport even
outside of active regions.Comment: Accepted for publication in A&
Detailed analysis of radiation data from the Gemini 4 and Gemini 7 proton-electron spectrometer experiments Final report, 13 Jun. 1967 - 30 Dec. 1968
Detailed analysis of radiation data from Gemini 4 and 7 proton-electron spectrometer experiment
On Aharonov-Casher bound states
In this work bound states for the Aharonov-Casher problem are considered.
According to Hagen's work on the exact equivalence between spin-1/2
Aharonov-Bohm and Aharonov-Casher effects, is known that the
term cannot be neglected in the
Hamiltonian if the spin of particle is considered. This term leads to the
existence of a singular potential at the origin. By modeling the problem by
boundary conditions at the origin which arises by the self-adjoint extension of
the Hamiltonian, we derive for the first time an expression for the bound state
energy of the Aharonov-Casher problem. As an application, we consider the
Aharonov-Casher plus a two-dimensional harmonic oscillator. We derive the
expression for the harmonic oscillator energies and compare it with the
expression obtained in the case without singularity. At the end, an approach
for determination of the self-adjoint extension parameter is given. In our
approach, the parameter is obtained essentially in terms of physics of the
problem.Comment: 11 pages, matches published versio
The Job Demands?Resources model: Challenges for future research
Motivation: The motivation of this overview is to present the state of the art of Job Demands-Resources (JD-R) model whilst integrating the various contributions to the special issue. Research purpose: To provide an overview of the JD-R model, which incorporates many possible working conditions and focuses on both negative and positive indicators of employee well-being. Moreover, the studies of the special issue were introduced. Research design: Qualitative and quantitative studies on the JD-R model were reviewed to enlighten the health and motivational processes suggested by the model. Main findings: Next to the confirmation of the two suggested processes of the JD-R model, the studies of the special issue showed that the model can be used to predict work-place bullying, incidences of upper respiratory track infection, work-based identity, and early retirement intentions. Moreover, whilst psychological safety climate could be considered as a hypothetical precursor of job demands and resources, compassion satisfaction moderated the health process of the model. Contribution/value-add: The findings of previous studies and the studies of the special issue were integrated in the JD-R model that can be used to predict well-being and performance at work. New avenues for future research were suggested. Practical/managerial implications: The JD-R model is a framework that can be used for organisations to improve employee health and motivation, whilst simultaneousl
On the influence of a Coulomb-like potential induced by the Lorentz symmetry breaking effects on the Harmonic Oscillator
In this work, we obtain bound states for a nonrelativistic spin-half neutral
particle under the influence of a Coulomb-like potential induced by the Lorentz
symmetry breaking effects. We present a new possible scenario of studying the
Lorentz symmetry breaking effects on a nonrelativistic quantum system defined
by a fixed space-like vector field parallel to the radial direction interacting
with a uniform magnetic field along the z-axis. Furthermore, we also discuss
the influence of a Coulomb-like potential induced by Lorentz symmetry violation
effects on the two-dimensional harmonic oscillator.Comment: 14 pages, no figure, this work has been accepted for publication in
The European Physical Journal Plu
Exposure to Fibres, Crystalline Silica, Silicon Carbide and Sulphur Dioxide in the Norwegian Silicon Carbide Industry
Objectives: The aim of this study was to assess personal exposure to fibres, crystalline silica, silicon carbide (SiC) and sulphur dioxide in the Norwegian SiC industry
Magnetic ground state and magnon-phonon interaction in multiferroic h-YMnO
Inelastic neutron scattering has been used to study the magneto-elastic
excitations in the multiferroic manganite hexagonal YMnO. An avoided
crossing is found between magnon and phonon modes close to the Brillouin zone
boundary in the -plane. Neutron polarization analysis reveals that this
mode has mixed magnon-phonon character. An external magnetic field along the
-axis is observed to cause a linear field-induced splitting of one of the
spin wave branches. A theoretical description is performed, using a Heisenberg
model of localized spins, acoustic phonon modes and a magneto-elastic coupling
via the single-ion magnetostriction. The model quantitatively reproduces the
dispersion and intensities of all modes in the full Brillouin zone, describes
the observed magnon-phonon hybridized modes, and quantifies the magneto-elastic
coupling. The combined information, including the field-induced magnon
splitting, allows us to exclude several of the earlier proposed models and
point to the correct magnetic ground state symmetry, and provides an effective
dynamic model relevant for the multiferroic hexagonal manganites.Comment: 12 pages, 10 figure
Accelerated particle beams in a 3D simulation of the quiet Sun. Lower atmospheric spectral diagnostics
Nanoflare heating through small-scale magnetic reconnection events is one of
the prime candidates to explain heating of the solar corona. However, direct
signatures of nanoflares are difficult to determine, and unambiguous
observational evidence is still lacking. Numerical models that include
accelerated electrons and can reproduce flaring conditions are essential in
understanding how low-energetic events act as a heating mechanism of the
corona, and how such events are able to produce signatures in the spectral
lines that can be detected through observations. We investigate the effects of
accelerated electrons in synthetic spectra from a 3D radiative
magnetohydrodynamics simulation to better understand small-scale heating events
and their impact on the solar atmosphere. We synthesised the chromospheric Ca
II and Mg II lines and the transition region Si IV resonance lines from a quiet
Sun numerical simulation that includes accelerated electrons. We calculated the
contribution function to the intensity to better understand how the lines are
formed, and what factors are contributing to the detailed shape of the spectral
profiles. The synthetic spectra are highly affected by variations in
temperature and vertical velocity. Beam heating exceeds conductive heating at
the heights where the spectral lines form, indicating that the electrons should
contribute to the heating of the lower atmosphere and hence affect the line
profiles. However, we find that it is difficult to determine specific
signatures from the non-thermal electrons due to the complexity of the
atmospheric response to the heating in combination with the relatively low
energy output (~1e21 erg/s). Even so, our results contribute to understanding
small-scale heating events in the solar atmosphere, and give further guidance
to future observations
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