1,053 research outputs found
Logarithmic perturbation theory for radial Klein-Gordon equation with screened Coulomb potentials via expansions
The explicit semiclassical treatment of logarithmic perturbation theory for
the bound-state problem within the framework of the radial Klein-Gordon
equation with attractive real-analytic screened Coulomb potentials, contained
time-component of a Lorentz four-vector and a Lorentz-scalar term, is
developed. Based upon -expansions and suitable quantization conditions a
new procedure for deriving perturbation expansions is offered. Avoiding
disadvantages of the standard approach, new handy recursion formulae with the
same simple form both for ground and excited states have been obtained. As an
example, the perturbation expansions for the energy eigenvalues for the
Hulth\'en potential containing the vector part as well as the scalar component
are considered.Comment: 14 pages, to be submitted to Journal of Physics
Simulation-Based Investigation of a Model for the Interaction Between Stellar Magnetospheres and Circumstellar Accretion Disks
We examine, parametrically, the interaction between the magnetosphere of a
rotating, young stellar object (YSO) and a circumstellar accretion disk using
2.5-D (cylindrically symmetric) numerical magnetoydrodynamic simulations. The
interaction drives a collimated outflow, and we find that the jet formation
mechanism is robust. For variations in initial disk density of a factor of 16,
variations of stellar dipole strength of a factor of 4, and for various initial
conditions with respect to the disk truncation radius and the existence of a
disk field, outflows with similar morphologies were consistently produced.
Secondly, the system is self-regulating, where the outflow properties depend
relatively weakly on the parameters above. The large scale magnetic field
structure rapidly evolves to a configuration that removes angular momentum from
the disk at a rate that depends most strongly on the field and weakly on the
rotation rate of the foot-points of the field in the disk and the mass outflow
rate. Third, the simulated jets are episodic, with the timescale of jet
outbursts identical to the timescale of magnetically induced oscillations of
the inner edge of the disk. To better understand the physics controlling these
disk oscillations, we present a semi-analytical model and confirm that the
oscillation period is set by the spin down rate of the disk inner edge.
Finally, our simulations offer strong evidence that it is indeed the
interaction of the stellar magnetosphere with the disk, rather than some
primordial field in the disk itself, that is responsible for the formation of
jets from these systems.Comment: Accepted by ApJ; 34 pages, including 12 figures and 3 table
Recognising Desire: A psychosocial approach to understanding education policy implementation and effect
It is argued that in order to understand the ways in which teachers experience their work - including the idiosyncratic ways in which they respond to and implement mandated education policy - it is necessary to take account both of sociological and of psychological issues. The paper draws on original research with practising and beginning teachers, and on theories of social and psychic induction, to illustrate the potential benefits of this bipartisan approach for both teachers and researchers. Recognising the significance of (but somewhat arbitrary distinction between) structure and agency in teachersâ practical and ideological positionings, it is suggested that teachersâ responses to local and central policy changes are governed by a mix of pragmatism, social determinism and often hidden desires. It is the often underacknowledged strength of desire that may tip teachers into accepting and implementing policies with which they are not ideologically comfortable
Teacher agency in curriculum making: agents of change and spaces for manoeuvre
In the wake of new forms of curricular policy in many parts of the world, teachers are increasingly required to act as agents of change. And yet, teacher agency is under-theorised and often misconstrued in the educational change literature, wherein agency and change are seen as synonymous and positive. This paper addresses the issue of teacher agency in the context of an empirical study of curriculum making in schooling. Drawing upon the existing literature, we outline an ecological view of agency as an effect. These insights frame the analysis of a set of empirical data, derived from a research project about curriculum-making in a school and further education college in Scotland. Based upon the evidence, we argue that the extent to which teachers are able to achieve agency varies from context to context based upon certain environmental conditions of possibility and constraint, and that an important factor in this lies in the beliefs, values and attributes that teachers mobilise in relation to particular situations
Turbulent protostellar discs
Aspects of turbulence in protostellar accretion discs are being reviewed. The
emergence of dead zones due to poor ionization and alternatives to the
magneto-rotational instability are discussed. The coupling between dust and gas
in protostellar accretion discs is explained and turbulent drag is compared
with laminar drag in the Stokes and Epstein regimes. Finally, the significance
of magnetic field generation in turbulent discs is emphasized in connection
with driving outflows and with star-disc coupling.Comment: 16 pages, 7 figures, proceedings of Nobel Symposium 135: Physics of
Planetary System
Changing times in England: the influence on geography teachersâ professional practice
School geography in England has been characterised as a pendulum swinging between policies that emphasise curriculum and pedagogy alternately. In this paper, I illustrate the influence of these shifts on geography teacher's professional practice, by drawing on three âmomentsâ from my experience as a student, teacher and teacher educator. Barnett's description of teacher professionalism as a continuous project of âbeingâ illuminates how geography teachers can adapt to competing influences. It reflects teacher professionalism as an unfinished project, which is responsive, but not beholden, to shifting trends, and is informed by how teachers frame and enact policies. I argue that recognising these contextual factors is key to supporting geography teachers in âbeingâ geography education professionals. As education becomes increasingly competitive on a global scale, individual governments are looking internationally for âsolutionsâ to improve educational rankings. In this climate, the future of geography education will rest on how teachers react locally to international trends. Geography teacher educators can support this process by continuing to inform the field through meaningful geography education research, in particular in making the contextual factors of their research explicit. This can be supported through continued successful international collaboration in geography education research
Symmetries and reversing symmetries of toral automorphisms
Toral automorphisms, represented by unimodular integer matrices, are
investigated with respect to their symmetries and reversing symmetries. We
characterize the symmetry groups of GL(n,Z) matrices with simple spectrum
through their connection with unit groups in orders of algebraic number fields.
For the question of reversibility, we derive necessary conditions in terms of
the characteristic polynomial and the polynomial invariants. We also briefly
discuss extensions to (reversing) symmetries within affine transformations, to
PGL(n,Z) matrices, and to the more general setting of integer matrices beyond
the unimodular ones.Comment: 34 page
Towards understanding the phenotypes of myocardial involvement in the presence of self-limiting and sustained systemic inflammation: a magnetic resonance imaging study
Objective. To investigate the patterns of myocardial involvement in the presence of self-limiting and sustained systemic inflammation, using MRI
The Disk Wind in the Young Binaries and the Origin of the Cyclic Activity of Young Stars
We present results of numerical modeling of the cyclic brightness modulation
in the young binary systems with the eccentric orbits and low-mass secondary
components. Brightness variations of the primary is due to the periodical
extinction variations on the line-of-sight caused by the disk wind of the
secondary and a common envelope it produces. A matter distribution in the
envelope has been calculated in the ballistic approach. Calculations showed
that for the young binaries with the elliptic orbits parameters of the
photometric minima (their depth, duration and the shape of light curves) depend
not only on the disk wind parameters and an inclination of the binary orbit to
the line-of-sight but also on the longitude of the periastron. A modulation of
the scattered radiation of the common envelope with a phase of the orbital
period has been investigated in the single scattering approach. It is shown
that an amplitude of the modulation is maximal when the system is seen edge-on
and has also a non-zero value in the binaries observed pole-on. Possible
applications of the theory to the young stellar objects are discussed. In
particular, an attention is payed to a resemblance of the light curves in some
models with light curves of the objects suspected as candidates to FUORs.Comment: 18 pages, 9 figures, accepted by Astronomy Letter
School-based curriculum development in Scotland: Curriculum policy and enactment
Recent worldwide trends in curriculum policy have re-emphasised the role of teachers in school-based curriculum development. Scotland’s Curriculum for Excellence is typical of these trends, stressing that teachers are agents of change. This paper draws upon empirical data to explore school-based curriculum development in response to Curriculum for Excellence. We focus on two case studies – secondary schools within a single Scottish local education authority. In the paper we argue that the nature and extent of innovation in schools is dependent upon teachers being able to make sense of often complex and confusing curriculum policy, including the articulation of a clear vision about what such policy means for education within each school
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