702 research outputs found
On the entropy of plasmas described with regularized -distributions
In classical thermodynamics the entropy is an extensive quantity, i.e.\ the
sum of the entropies of two subsystems in equilibrium with each other is equal
to the entropy of the full system consisting of the two subsystems. The
extensitivity of entropy has been questioned in the context of a theoretical
foundation for the so-called -distributions, which describe plasma
constituents with power-law velocity distributions. We demonstrate here, by
employing the recently introduced {\it regularized -distributions},
that entropy can be defined as an extensive quantity even for such
power-law-like distributions that truncate exponentially.Comment: Preprint accepted for publication in Phys. Rev.
Energetic neutral atom fluxes from the heliosheath varying with the activity phase of the solar cycle
International audienceEnergetic neutral atoms (ENA's) which are produced in the heliospheric interface can be used to remotely investigate this highly interesting, but poorly known region acting as buffer against the interstellar plasma. To optimally take advantage from this very promising observational technique, based on ENA flux measurements, one needs to know the spectral production rate of the ENA's in the heliosheath and about the foreground ENA contaminations originating in the inner heliosphere, e.g. inside the termination shock. Heliosheath ENA's with energies of about a few KeV originate from charge exchange reactions of H-atoms both with the shocked solar wind protons and with pick-up protons downstream of the termination shock. Inner heliospheric ENA's detectable at the Earth can only originate from H charge exchange reactions with pick-up protons. In this article we calculate on the basis of the five-fluid Bonn model the time-dependent ENA fluxes that are connected with these three sources and compare them. It will be demonstrated that the heliosheath ENA fluxes dominate from nearly all directions over the inner heliospheric ENA fluxes, though the best chances to disentangle the contributions appear in upwind and downwind direction at specific periods of the solar activity cycle
Comparing various multi-component global heliosphere models
Modeling of the global heliosphere seeks to investigate the interaction of
the solar wind with the partially ionized local interstellar medium. Models
that treat neutral hydrogen self-consistently and in great detail, together
with the plasma, but that neglect magnetic fields, constitute a sub-category
within global heliospheric models. There are several different modeling
strategies used for this sub-category in the literature. Differences and
commonalities in the modeling results from different strategies are pointed
out. Plasma-only models and fully self-consistent models from four research
groups, for which the neutral species is modeled with either one, three, or
four fluids, or else kinetically, are run with the same boundary parameters and
equations. They are compared to each other with respect to the locations of key
heliospheric boundary locations and with respect to the neutral hydrogen
content throughout the heliosphere. In many respects, the models' predictions
are similar. In particular, the locations of the termination shock agree to
within 7% in the nose direction and to within 14% in the downwind direction.
The nose locations of the heliopause agree to within 5%. The filtration of
neutral hydrogen from the interstellar medium into the inner heliosphere,
however, is model dependent, as are other neutral results including the
hydrogen wall. These differences are closely linked to the strength of the
interstellar bow shock. The comparison also underlines that it is critical to
include neutral hydrogen into global heliospheric models.Comment: 10 pages, 4 figures, submitted to a special section at A&A of an ISSI
team "Determination of the physical Hydrogen parameters of the LIC from
within the Heliosphere
Flux and field line conservation in 3--D nonideal MHD flows: Remarks about criteria for 3--D reconnection without magnetic neutral points
We make some remarks on reconnection in plasmas and want to present some
calculations related to the problem of finding velocity fields which conserve
magnetic flux or at least magnetic field lines. Hereby we start from views and
definitions of ideal and non-ideal flows on one hand, and of reconnective and
non-reconnective plasma dynamics on the other hand. Our considerations give
additional insights into the discussion on violations of the frozen--in field
concept which started recently with the papers by Baranov & Fahr (2003a;
2003b). We find a correlation between the nonidealness which is given by a
generalized form of the Ohm's law and a general transporting velocity, which is
field line conserving.Comment: 9 pages, 2 figures, submitted to Solar Physic
The effects of a kappa-distribution in the heliosheath on the global heliosphere and ENA flux at 1 AU
We investigate heliosheath energetic neutral atom (ENA) fluxes at keV
energies, by assuming that the heliosheath proton distribution can be
approximated by a kappa-distribution. The choice of the kappa parameter derives
from observational data of the solar wind (SW). This has direct applications to
the upcoming IBEX mission. We will look at all-sky ENA maps within the IBEX
energy range (10 eV to 6 keV), as well as ENA energy spectra in several
directions. We find that the use of kappa, as opposed to a Maxwellian, gives
rise to greatly increased ENA fluxes above 1 keV, while medium energy fluxes
are somewhat reduced. We show how IBEX data can be used to estimate the
spectral slope in the heliosheath, and that the use of kappa reduces the
differences between ENA maps at different energies. We also investigate the
effect introducing a kappa-distribution has on the global interaction between
the SW and the local interstellar medium (LISM), and find that there is
generally an increase in energy transport from the heliosphere into the LISM,
due to the modified profile of ENA's energies. This results in a termination
shock that moves out by 4 AU, a heliopause that moves in by 9 AU and a bow
shock 25 AU farther out, in the nose direction
Diffractive beam splitter characterization via a power-recycled interferometer
We used the high-precision laser interferometer technique of power recycling to characterize the optical loss of an all-reflective grating beam splitter. This beam splitter was used to set up a Michelson interferometer with a power-recycling resonator with a finesse of 883. Analyzing the results obtained, we determined the beam splitter's total optical loss to be (0.193+/-0.019)%. Low loss all-reflective beam splitters might find application in future high-power laser interferometers for the detection of gravitational waves
Neutral H density at the termination shock: a consolidation of recent results
We discuss a consolidation of determinations of the density of neutral
interstellar H at the nose of the termination shock carried out with the use of
various data sets, techniques, and modeling approaches. In particular, we focus
on the determination of this density based on observations of H pickup ions on
Ulysses during its aphelion passage through the ecliptic plane. We discuss in
greater detail a novel method of determination of the density from these
measurements and review the results from its application to actual data. The H
density at TS derived from this analysis is equal to 0.087 \pm 0.022 cm-3, and
when all relevant determinations are taken into account, the consolidated
density is obtained at 0.09 \pm 0.022 cm-3. The density of H in CHISM based on
literature values of filtration factor is then calculated at 0.16 \pm 0.04
cm-3.Comment: Submitted to Space Science Review
Assessing roost disturbance of straw-coloured fruit bats (Eidolon helvum) through tri-axial acceleration
The disturbance of wildlife by humans is a worldwide phenomenon that contributes to the loss of biodiversity. It can impact animals' behaviour and physiology, and this can lead to changes in species distribution and richness. Wildlife disturbance has mostly been assessed through direct observation. However, advances in bio-logging provide a new range of sensors that may allow measuring disturbance of animals with high precision and remotely, and reducing the effects of human observers. We used tri-axial accelerometers to identify daytime flights of roosting straw-coloured fruit bats (Eidolon helvum), which were used as a proxy for roost disturbance. This bat species roosts on trees in large numbers (often reaching hundreds of thousands of animals), making them highly vulnerable to disturbance. We captured and tagged 46 straw-coloured fruit bats with dataloggers, containing a global positioning system (GPS) and an accelerometer, in five roosts in Ghana, Burkina Faso and Zambia. Daytime roost flights were identified from accelerometer signatures and modelled against our activity in the roosts during the days of trapping, as a predictor of roost disturbance, and natural stressors (solar irradiance, precipitation and wind speed). We found that daytime roost flight probability increased during days of trapping and with increasing solar irradiance (which may reflect the search for shade to prevent overheating). Our results validate the use of accelerometers to measure roost disturbance of straw-coloured fruit bats and suggest that these devices may be very useful in conservation monitoring programs for large fruit bat species.info:eu-repo/semantics/publishedVersio
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