4,424 research outputs found
Magnetic flux emergence in fast rotating stars
Fast rotating cool stars are characterised by high magnetic activity levels
and frequently show dark spots up to polar latitudes. Their distinctive surface
distributions of magnetic flux are investigated in the context of the
solar-stellar connection by applying the solar flux eruption and surface flux
transport models to stars with different rotation rates, mass, and evolutionary
stage. The rise of magnetic flux tubes through the convection zone is primarily
buoyancy-driven, though their evolution can be strongly affected by the
Coriolis force. The poleward deflection of the tube's trajectory increases with
the stellar rotation rate, which provides an explanation for magnetic flux
eruption at high latitudes. The formation of proper polar spots likely requires
the assistance of meridional flows both before and after the eruption of
magnetic flux on the stellar surface. Since small radiative cores support the
eruption of flux tubes at high latitudes, low-mass pre-main sequence stars are
predicted to show high mean latitudes of flux emergence. In addition to flux
eruption at high latitudes, main sequence components of close binary systems
show spot distributions which are non-uniform in longitude. Yet these
`preferred longitudes' of flux eruption are expected to vanish beyond a certain
post-main sequence evolutionary stage.Comment: 8 pages, 12 figures, in Memorie della Societa Astronomica Italiana
Vol. 78 n. 2, p. 27
Thoughts about recent education reform in India: Is there a tendency towards privatisation in elementary education?
The debate in India about the Right to Education Bill 2005 is an example for the basic question in education reform: Is education to be provided by the state or by private actors? With this bill the Government of India (GoI) suggests it\u27s programme to implement the "right to education", which has become the 86th amendment to the constitution in 2002. It guarantees free and compulsory education for all children in the age of 6-14. There is a rapid increase in private initiative in order to fill insufficient government provision of quality education. But is the state enforcing privatisation of education? The debate about the Right to Education Bill shows an ambivalent attitude of the GoI towards private schools: They are seen as a means to achieve Education for All through a reservation policy for children from low socio-economic strata on the one hand and tries to control them more in order to decrease the number of unrecognised schools. Critics of the current education policy accuse the GoI of a lack of strength to create a common school system, in their view the only way to make the constitutional right a reality. On this backdrop the article discusses statements in favour and against an increasing role of private actors in education and concludes that the noble idea of a right to education as amended to the constitution can not be fulfilled if the state does not take its primary responsibility for the provision of quality education to every child serious. (DIPF/Orig.)Die Debatte in Indien anlässlich der "Right to Education Bill 2005" ist ein Beispiel für eine Auseinandersetzung über eine grundlegende Frage der Bildungsreform: Ist es der Staat oder sind es private Akteure die für Bildung verantwortlich sind? Die neue Gesetzesvorlage skizziert das Programm zur Umsetzung des Rechts auf Bildung. Dieses Recht wurde 2002 in die Verfassung aufgenommen und garantiert jedem Kind im Alter von 6-14 Jahren frei zugängliche Bildung unter einer allgemeinen Schulpflicht. Gleichzeitig wächst die Zahl der privaten Schulen immer weiter, vor allem dort wo der Staat keine qualitativ hochwertige Bildung anbietet. Heißt das, dass der Staat sich in die Richtung einer Privatisierung der Bildung bewegt? Die Debatte zeigt, dass der indische Staat eine ambivalente Haltung gegenüber den privaten Schulen einnimmt: Auf der einen Seite werden sie als ein Weg gesehen "Education For All" zu erreichen. Das zeigt die angedachte Regelung der Reservierung von Plätzen in Privatschulen für Kinder aus ärmeren Familien. Auf der anderen Seite sieht der Entwurf eine stärkere Kontrolle über die privaten Träger vor, um die Zahl der Privatschulen, die ohne staatliche Anerkennung arbeiten, zu verringern. KritikerInnen dieser Pläne der Regierung fordern die Einführung eines allgemeinen Schulsystems zur Überwindung der Stratifikation, die durch die verschiedenen Schulen verstärkt wird. Vor diesem Hintergrund zeigt der Artikel das Für und Wider einer Aktivität von Privatschulen auf und kommt zu dem Schluss, dass die noble Idee eines "Rechts auf Bildung" nur umgesetzt werden kann, wenn der Staat seine eigentliche Verantwortung für Bildung ernst nimmt. (DIPF/Orig.
Dynamics of magnetic flux tubes in close binary stars I. Equilibrium and stability properties
Surface reconstructions of active close binary stars based on photometric and
spectroscopic observations reveal non-uniform starspot distributions, which
indicate the existence of preferred spot longitudes (with respect to the
companion star). We consider the equilibrium and linear stability of toroidal
magnetic flux tubes in close binaries to examine whether tidal effects are
capable to initiate the formation of rising flux loops at preferred longitudes
near the bottom of the stellar convection zone. The tidal force and the
deviation of the stellar structure from spherical symmetry are treated in
lowest-order perturbation theory assuming synchronised close binaries with
orbital periods of a few days. The frequency, growth time, and spatial
structure of linear eigenmodes are determined by a stability analysis. We find
that, despite their small magnitude, tidal effects can lead to a considerable
longitudinal asymmetry in the formation probability of flux loops, since the
breaking of the axial symmetry due to the presence of the companion star is
reinforced by the sensitive dependence of the stability properties on the
stellar stratification and by resonance effects. The orientation of preferred
longitudes of loop formation depends on the equilibrium configuration and the
wave number of the dominating eigenmode. The change of the growth times of
unstable modes with respect to the case of a single star is very small.Comment: 11 pages, 11 figures, accepted for publication in A&
On the physics behind the form factor ratio
We point out that there exist two natural definitions of the nucleon
magnetization densities : the density introduced in Kelly's
phenomenological analysis and theoretically more standard one . We
can derive an explicit analytical relation between them, although Kelly's
density is more useful to disentangle the physical origin of the different
dependence of the Sachs electric and magnetic form factors of the
nucleon. We evaluate both of and as well as the
charge density of the proton within the framework of the chiral
quark soliton model, to find a noticeable qualitative difference between
and , which is just consistent with Kelly's result
obtained from the empirical information on the Sachs electric and magnetic form
factors of the proton.Comment: 12 pages, 5 figures. version to appear in J. Phys. G.: Nucl. Part.
Phy
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