1,221 research outputs found
High orders of the perturbation theory for hydrogen atom in magnetic field
The states of hydrogen atom with principal quantum number and zero
magnetic quantum number in constant homogeneous magnetic field are
considered. The coefficients of energy eigenvalues expansion up to 75th order
in powers of are obtained for these states. The series for energy
eigenvalues and wave functions are summed up to values of the order
of atomic magnetic field. The calculations are based on generalization of the
moment method, which may be used in other cases of the hydrogen atom
perturbation by a polynomial in coordinates potential.Comment: 16 pages, LaTeX, 6 figures (ps, eps
The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System
We describe the layout and unique features of the focal plane system for
MIRI. We begin with the detector array and its readout integrated circuit
(combining the amplifier unit cells and the multiplexer), the electronics, and
the steps by which the data collection is controlled and the output signals are
digitized and delivered to the JWST spacecraft electronics system. We then
discuss the operation of this MIRI data system, including detector readout
patterns, operation of subarrays, and data formats. Finally, we summarize the
performance of the system, including remaining anomalies that need to be
corrected in the data pipeline
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
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
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
The development of Scotlandâs Curriculum for Excellence: Amnesia and DĂ©jĂ Vu
Scotlandâs new Curriculum for Excellence (CfE) has been widely acknowledged as the most significant educational development in a generation, with the potential to transform learning and teaching in Scottish schools. In common with recent developments elsewhere, CfE seeks to re-engage teachers with processes of curriculum development, to place learning at the heart of the curriculum and to change engrained practices of schooling. This article draws upon well-established curriculum theory (notably the work of both Lawrence Stenhouse and A.V. Kelly) to analyse the new curriculum. We argue that by neglecting to take account of such theory, the curricular offering proposed by CfE is subject to a number of significant structural contradictions which may affect the impact that it ultimately exerts on learning and teaching; in effect, by ignoring the lessons of the past, CfE runs the risk of undermining the potential for real change
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
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