8,491 research outputs found
Coronal versus photospheric abundances of stars with different activity levels
We report a detailed analysis of the coronal abundance of 4 stars with
varying levels of activity and with accurately known photospheric abundances.
The coronal abundance is determined here using a line flux analysis and a full
determination of the differential emission measure. Photospheric abundance
values are taken from literature works. Previous coronal abundance
determinations have generally been compared to solar photospheric abundances;
from this a number of general properties have been inferred, such as the
presence of a coronal metal depletion with an inverse First Ionization
Potential correlated with activity level. Here we show that, when coronal
abundances are compared with real photospheric values for the individual stars,
the resulting pattern can be very different. Also, we present evidence that, in
some cases, the coronal metal abundance may not be uniform in the corona; in
particular it can vary with the temperature of the emitting plasma.Comment: 10 pages, Online material: 8 pages (online material is included in
the file). Accepted by A&
The Formation of non-Keplerian Rings of Matter about Compact Stars
The formation of energetic rings of matter in a Kerr spacetime with an
outward pointing acceleration field does not appear to have previously been
noted as a relativistic effect. In this paper we show that such rings are a
gravimagneto effect with no Newtonian analog, and that they do not occur in the
static limit. The energy efficiency of these rings can, depending of the
strength of the acceleration field, be much greater than that of Keplerian
disks. The rings rotate in a direction opposite to that of compact star about
which they form. The size and energy efficiency of the rings depend on the
fundamental parameters of the spacetime as well as the strength the
acceleration field.Comment: 19 pages, 7 figures, 1 diagram. Figures are included in the text
using the "graphicx" package. If you do not have this package you can use
epsfig, or another package as long as you alter the tex file appropriately.
Alternatively you could print the figures out seperatel
Shotguns vs Lasers: Identifying barriers and facilitators to scaling-up plant molecular farming for high-value health products.
Plant molecular farming (PMF) is a convenient and cost-effective way to produce high-value recombinant proteins that can be used in the production of a range of health products, from pharmaceutical therapeutics to cosmetic products. New plant breeding techniques (NPBTs) provide a means to enhance PMF systems more quickly and with greater precision than ever before. However, the feasibility, regulatory standing and social acceptability of both PMF and NPBTs are in question. This paper explores the perceptions of key stakeholders on two European Union (EU) Horizon 2020 programmes-Pharma-Factory and Newcotiana-towards the barriers and facilitators of PMF and NPBTs in Europe. One-on-one qualitative interviews were undertaken with N = 20 individuals involved in one or both of the two projects at 16 institutions in seven countries (Belgium, France, Germany, Italy, Israel, Spain and the UK). The findings indicate that the current EU regulatory environment and the perception of the public towards biotechnology are seen as the main barriers to scaling-up PMF and NPBTs. Competition from existing systems and the lack of plant-specific regulations likewise present challenges for PMF developing beyond its current niche. However, respondents felt that the communication of the benefits and purpose of NPBT PMF could provide a platform for improving the social acceptance of genetic modification. The importance of the media in this process was highlighted. This article also uses the multi-level perspective to explore the ways in which NPBTs are being legitimated by interested parties and the systemic factors that have shaped and are continuing to shape the development of PMF in Europe
Onset of Fast Magnetic Reconnection in Partially Ionized Gases
We consider quasi-stationary two-dimensional magnetic reconnection in a
partially ionized incompressible plasma. We find that when the plasma is weakly
ionized and the collisions between the ions and the neutral particles are
significant, the transition to fast collisionless reconnection due to the Hall
effect in the generalized Ohm's law is expected to occur at much lower values
of the Lundquist number, as compared to a fully ionized plasma case. We
estimate that these conditions for fast reconnection are satisfied in molecular
clouds and in protostellar disks.Comment: 19 pages, 1 figure, 1 tabl
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